If I owned the promotion, and "purchased" the IP, I would use that as an in game reason to increase my merchandise quality (selling best ofs of the promotion, T-Shirts of that promotion etc.) and if I ever used the old promotion's names for an event, I would edit it to be of higher importance than a new event would be.
I suppose, if you feel the purchase adds to the legitimacy of your own promotion, I would add to my promotion's prestige. If, in-universe, the purchase shows how dominant the promotion is (ala when WWE bought WCW and ECW) I would add to my promotion's momentum rating.
If this promotion has workers that aren't out of the business, I would hire them for "legend" style segments. If I were to "use" old footage on my television show, I would do so by using these workers in off-screen angles, which might not be the correct use for that, but I would consider old footage a type of hype package, I guess.
If the purchasing of the promotion would offend or make people feel betrayed, I would add those relationships to the owner of the company (Not a wrestling example, but when MJ bought the Beatles catalogue, he and Paul McCartney went from friends to enemies real quick.)
Likewise, if the bought promotion is treated with dignity and respect, and has high quality products of it put out, you may endear the workers of that promotion to your owner.
If you wanted to showcase a worker of this old promotion in a more direct way, you can edit some money out of your promotion to give a wrestler a bump is popularity and respect (A dvd is put out of a worker's greatest matches and promos with commentary on his influence in the industry.)