Is there any way to get inside on this version? I guess it would be pointless since all costumes are already unlocked, but it's so weird having that part of the map permanently unexplored.

This particular change may be revertable via an already existing(?) or future mod, I imagine.

A mod for it has been around for a few years, made by ResidentEvilArtist and MartinBiohazard.

ResidentEvilArtist's mod is the better one, but the download link has expired. I have it on my PC though.

Mod from ResidentEvilArtist's:
https://www.moddb.com/mods/resident-evil-3-boutique-room-for-restoration-patch/downloads/the-boutique-is-available-for-re-3-restoration-patch-v0-8

Mod from MartinBiohazard:
http://re123.bplaced.net/board/viewtopic.php?f=23&t=60

In both cases, you must extract the game files. BioFAT and RE3ROFSBE cannot extract the rofs11.dat file correctly. The game will crash in the RPD. Therefore, do not edit the entry for rofs11.dat in bio.ini.

Here is the german version:
https://www.nexusmods.com/residentevil3nemesis/mods/48?tab=description

RPD crash fix for me was to swap files with the gamecube verison . NOT introducing new files types only replacing existing . except for the update files 1.1.0 i think ? might of done it on the USA ver also dont remember ? now knowing it was rofs11 you can narrow down exactly what needs to be replaced