When I spoke to Motability about this they just said it had to be done by a reputable company and be removable if required, I asked if it needed removing before hand back and they said not normally, only if specifically contacted by them beforehand and asked in writing to have them removed.
I did wonder what the criteria would be for that but the nice lady explained b4 I could ask, if a dealer that was interested in purchasing the car at lease end had contacted Motability and asked for modifications to be removed, otherwise it didn’t matter.