I had a parastomal hernia and also had it fixed with my colostomy reversal. I think when things are moving through that area is when I noticed it bigger or painful.
Laying on my back for awhile helped a ton.
Make sure to ask a lot of questions around how they are planning to fix the hernia. That polypropylene mesh is causing many problems for folks. My surgeon used a bio mesh (body absorbs in 6 months) gore bio a and it has been fine so far (had it for about a year) there are others in that category as well. And if he has a technique he uses that works and holds up without any mesh or if you don’t need it, even better from what I have heard.