This is SOMEWHAT true, I've had some success with switching over from one tileset map to the other, going by what Game Freak originally did with fire red. I noticed that they carefully only used overworld tiles from tileset 0 when switching between maps NORMALLY, but going up Route 1 to Viridian city, the tileset abruptly changes at the connection point from 01 (pallet town) to 02 (viridian city), but anyone who's played the game knows, for some reason, the tiles from tileset 1 don't seem to impose. Why? Because nintendo was sneaky. They carefully made sure that for at least seven to ten tiles up from route 1, that no custom viridian city tiles would be used.
By the time you see custom tile'd things like houses, you've gone up a significant enough portion of the map that the memory dump loads them with viridian's tileset, and not glitching between that and pallet's tileset.
TL;DR: If you wish to switch between tilesets, do what nintendo did, make sure there's only tiles from tileset 0 for around ten tiles either way between transitions. I didn't exactly go counting them, so it might be slightly more or less. You'll need some trial and error to test this out possibly.
It shouldn't glitch if you give the ROM enough space to load the new tileset onto the custom tiles on the map.
Sorry if any of this was at all confusing.