These can't be converted perfectly to 48x48 from 32x32 without being redrawn unfortunately. MV/MZ takes base size 48x48 tiles and 48/32 = 1.5. You end up with a lot of distorted pixels if you try to scale the tiles up from 32x32 to 48x48. On my Patreon, the $5 tier is able to make a tile request for upcoming sets. All tiers are able to vote on set themes.