I would use "repo'd." I use the apostrophe for some awkward words like that.
For example, if somebody gets RIF'd from their job, you could do it like "RIF-ed" or "RIFed" or "RIF'd."
I always try to think in terms of what will look best in terms of the reader of the transcript. Verbatim transcription can sure be a tough nut to crack sometimes.
I like it when they say "he axed a question." To this day, I have never used "axed" and always use "asked," but someday, if they catch me in a bad mood....
Here's one reference:
When a word ends in a, i, or o, some writers prefer to form the past tense by adding 'd; other writers add the usual ed. Thus, you may see any of the following forms: subpoena'd, subpoenaed, ski'd, skied, echo'd, echoed.
Also, I would invite you to check out our WONDERFUL, WONDERFUL, WONDERFUL "Comma Conundrums & Other Punctuation Perplexities" section of this form: Comma Conundrums & Other Punctuation Perplexities
I know I have asked my fair share of questions in that area of this forum. There are some very august and seasoned members of this forum who visit that area of the forum and share their bits of wisdom.
IMO this is one where it's not going to look good either way. I'd probably put repo'd because people do use bad slang in legal proceedings all the time and because that's what my high school English teacher would have taught.
I don't think there's a wrong or right here, actually.
I also have teacher certification in English 6-12. When words are slanged, the custom is to use the hyphen. Example: Do not (don't). If you have a word with the re in front, re is a prefix, so nothing special is done. Example: possess - repossess; start; restart. You wouldn't put re-start.
So using basic English rules, reposessed - slang it, repo'd.