This is something I’ve been working on for a while. FE7’s snow castle tileset has been improved, I’ve added new tiles for carpets and stairs, and edited the palette to be more FE8 suitable.
Disclaimer: Various tiles have been moved around (and some useless carpet tiles have been removed), therefore your existing maps made with this tileset may have minor issues.
If you want to learn how to insert tilesets, look at this tutorial by DerTheVaporeon.
Free to use with credit.