I can't seem to add ice physics indoors

When using HM, I selected "Choose an object," selected the floor tiles, clicked on the "edit" button, right clicked the tiles and attempted to change the numbers. For some reason, it doesn't update to the number I changed it to. Why is it like that?

I think that there are different tile sets that the game uses per dungeon. So in the ice dungeon you have these ice tiles, but not in the red platform dungeon with the red cane.

But I don't know how to pick which tile set you can use on the fly.

the ice tile platforms in turtle rock will look like water tiles if I recall correctly. you would have to change gfx to get the ice tiles.

"Ice phisics" indoors is more complex than you might think. The game will not allow you to just add ice in any room. It is also not recomended to edit objects at all when trying to make ice. The goal of editing an object is to make new previosuly non existant objects.

For ice to actually work indoors you will need existing ice objects and a correct gfx set, which will indeed load the correct tiles and the correct property of them. This is not at all easy since the ice is a "moving object" and will load from special gfx set which handles the loading of three frames to indicate ice-glitter.

Sticking to the rooms which have ice in the original game is your best bet to not glitch this out. You can see this when putting ice into some other dungeons, specially the water dungeon. It will display ice (on correct gfx), but once you stand on it, it will have water property.

The ice and water dungeons are specific. These two simply are not neutral, since shallow water (also moving also specific) will be problematic to be compatible with any dungeon, so is the draining of water channels. It is thus recomended to use existing original rooms for water and ice dungeons.

When using HM, I selected "Choose an object," selected the floor tiles, clicked on the "edit" button,

Ok so far.

right clicked the tiles and attempted to change the numbers.

Here's you problem. You don't right click. You left click on the gfx set, then set the Palette and then left click on the object to draw from gfx tiles onto the object to give it a new look. But like said this is not recomended. Since you will be making new tiles, which don't exist in original game.

You can not change the type of selected element in the gfx set (doable in hex only) - also not recomended to do, since you do not change the type of the obejct itself but of the location onto which multiple gfx sets are loaded. So the only recomended tile type to change is in the neutral gfx set, the one which has a big chest in it, since this is loaded in every dungeon and is thus the same on all gfx numbers.