Current questions and answers regarding the map editor.

so that the object's texture looks like a warrior's tomb, but the object functions like a dungeon.

There is also an alternative option using scripts: disable the standard properties of the warrior's tomb, place a dungeon somewhere in a secluded location on the map, and when entering the tomb, use the function
MakeHeroInteractWithObject(HERO_NAME, DUNGEON_NAME);

the transformation should look like dividing the troops in half (i.e., the same window with the option to edit the number of warriors), while 350 is charged from the player for each warrior.

I doubt that this can be done with the available tools; there is a simplified option to use TalkBox with a choice of answers "transform 20% of warriors," 40%, 60%, 80%, 100% - I do this for similar things.