Giddish also appeared in another SVU episode before joining SVU as a regular.

Kelli Giddish apeared in an episode of L&O Criminal Intent, before becoming a regular on SVU.

Similarly, the late James Trebhorn played defense lawyer Charles Garnett In 5 episodes before playing an executioner doctor in his final episode.
James Rebhorn actually also appeared as serial killer Albert Cheney in season 2's "Vengeance",
before
his recurring stint as Charles Garnett.

There is a term I have read which describes L&O guest stars who appear in different roles in multiple episodes: "Repeat Offenders"
Lindsay Crouse is not the only L&O Repeat Offender who played two different roles of the same type (judge). A bearded Ron Leibman played defense lawyer Paul Kopell in Season 5's "House Counsel," a terrific episode which pits Jack against his friend who manages to defeat him several times during a case before Jack finally bests him at the end. Then, in Season 11's "Amends," he played a clean-shaven Barry Nathanson, another defense lawyer. Oddly, less than a year later, Leibman (again, clean shaven) would appear in 4 SVU episodes as ADA Cabot's immediate boss, playing a different character.
To me, the most versatile guest star in L&O is David (Wolos-)Fonteno, who played 6 vastly different roles in 6 different episodes spread out over 10 years before getting "promoted" to a judge in his 7th appearance. He would play that same judge 2 more times in the next 8 years (before playing another judge 10 times in "The Good Wife" series!).

I recall Frank Converse (co-star of
Movin' On
in the 70's) appearing in several episodes. Two of them dealt with horses, but he was a different character in every episode. He was interviewed by Lennie in three of the episodes:
In S2 E11 (1991, Logan/Ceretta), he played Gary Wallace, his first of five appearances as different characters (1991-2004).
In S6 E11 (1996, Briscoe/Curtis), he played a suspect.
In S9 E22 (1999, Briscoe/Curtis), he played Mr. Kelly, his 3rd of five appearances as different characters.
In S14 E23 (2004, Briscoe/Green) he played a stable manager, his 4th appearance since 1991. In S2E11 he played the suspect, who was also in the horse business.
In S19 E4 (2008, Lupo/Bernard) he played Wayne Hardy, his final appearance.
More unimportant trivia: 2004 was Lennie's last season. S14 E23 was his next-to-last episode. As you noted, S2 E2 Jerry Orbach appeared as defense lawyer Frank Lehrman, and he first appeared full time as Lennie in S3 E9.
While we're at it, I recall the same actress (Lindsay Crouse) playing two different judges. She first appeared as a non-judge in S3 E14.
What was fun about this actress is that the first judge died in S10 E03. Her final appearance on L&O was six years later in S16 E01 as another judge. I watch
Supernatural
, and one of the truisms there is that no one really ever dies (several characters have died and come back to life). The same can be said to a degree for
L&O
.
She went on to play a third judge in 7 episodes of
SVU
. I'd say she was typecast!
Ignoring politics doesn't mean politics will ignore you.
-Pericles paraphrased in <100 characters

James Trebhorn also played a serial killer of sorts! His wife would give him alibis, but evidence found in his apartment showed skeleton keys, duck tape, and some kind of electrician ID used to kill a woman! It was a convoluted story where she was called to her apartment from her parent's home in another state! The mom was called exaggerating knowing all her friends while the defense attorney went down names in the girl's phone book!

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Me, too. Besides Annie Parisse appearing as a stripper before becoming an ADA, Jerry Orbach played a defense lawyer before becoming Briscoe. Merkerson was the mother of an infant victim before playing Van Buren. Even Milena Govich appeared in a tiny guest role before becoming the short-lived, awful Nina Cassady. Those guest role "tryouts" for taking a starring role (and yes, Sisto's promotion was achieved in record time LOL!) have taken place in the other L&O series, sometimes appearing as a guest in one series before starring in another one.
I also find it pretty funny when a guest star who appeared in the same role in several episodes (i.e. a defense lawyer or a judge) then appears in a different guest role. Ron McLarty, who appeared 4 times as the despised Judge Wright, then played a librarian in his next appearance. Similarly, the late James Trebhorn played defense lawyer Charles Garnett In 5 episodes before playing an executioner doctor in his final episode.

LOL the only "sequel" of sorts to that was the stripper returning 3 seasons later as McCoy's ADA. I get a kick out of the same actors appearing as one person then appearing as a regular. I think it was the last episode of S17 and the first episode of S18 where Jeremy Sisto did this. Shortest turnaround ever on the show.
Ignoring politics doesn't mean politics will ignore you.
-Pericles paraphrased in <100 characters

You are referring to Season 12's "Attorney Client," starring guest star Peter Friedman in the title role. It would have been nice to see a sequel to that episode, I agree.
But the one episode I would have loved seeing a sequel to is Season 6's "Corpus Delicti." That was the one which began, oddly, with a dead horse (and some really funny lines from Briscoe), and transformed into a case Jack tried without a dead body. Jack was losing the case and provoked a mistrial (intentionally or not, that's the question) in order to get another chance at a trial with better evidence - the victim's body was discovered at the very end of the episode, Jack learned.
This episode was ripe for a sequel, one which includes a retrial after Jack battles the defense and the judge (and Adam, who also suspected Jack of provoking a mistrial). I could also see this sequel as a way to get Jill Hennessey back as a guest star (in Season 7 or later), perhaps as part of a flashback to include scenes with her not shown in the original episode.