They say "stiffening panel" on the back side of them. I think its part of the rear tire well. I could have attempted to do it myself, but i dont have the space nor do I think I would be strong enough to pull a tire and wheel off myself.Not sure what these are...having a hard time picturing where they go, or what they look like. Probably do need to pull some clips and pull panels away to make these fit like they did out of the factory....rally armor mudflaps are the same way.
Why not do it yourself though?
Ive put mudguards on a 16 Crosstrek, 14 and 17 Forester and never had to remove anything from the rear. OEM and Rockblocs go right over the shield/plastic inner liners in the rear. Usually you just have to drill an extra hole. ON the foresters, you do have to remove a piece from the front that the mudguard takes the place of but its not a stiffening shield.Check out this link for installationhttps://techinfo.subaru.com/proxy/110103/pdf/110103-J1010SG300.pdf instructions for a forester but same thing as far as removal of stiffener shields but you may be able to find yours on line.