I have done the mansion overlay more than once. I gave up on one magnet overlay with the Siren & smoke as the orange area of colour was more like babyshit brown (Hand painted the damage instead).
IMHO
(a) You must be prepared to have the PF professionally clearcoated with two pack after applying the decal(s) I do not personally hold with Mylar as it will cause ball deflection and is impossible to apply crystal clear ie. without air inclusions which cause "misting" or "sparkle" from minute bubbles.
(b) The original Mansion inserts may well need to be cleaned and rebuilt up to flush with coats clear acrylic spray (blocking back between coats) before applying the overlay decal.
(c) SLIP on the decals on using diluted windex or water with a few drops of detergent. This "slipping" method is essential to get near perfect edge matching. CAREFULLY tamp dry & leave for 20-30 mins to set.
(d) You or an artist will most likely need to touch-paint back the black borders around the PF inserts as there are often chipped bits and imperfections in the decal extremities. If the decal(s) aren't exact, some work may be needed on coloured borders too; this does require much skill. Then it's off to the clearoaters.
(e) Buy or build the magnet protection fuse kit to prevent another disaster!
(f) For f*ck it's hard to do! Good luck finding a resto artist nearby.

Max