Not resists.
I created an all 70s suit as an example for my son's RP character.
Things that over write are such as slayers - get a nice weapon, but the downside is it's a snow ele slayer, overwrite it with demon/undead etc.
Hit spell effects overwrite each other, can't have hit magic arrow and hit lightning on the same weapon.
As a rule of thumb, if a certain combination is possible in game now, it's possible through imbuing.
+ skill jewellery has some restrictions on combinations, but they're the same groupings as that already used in loot drops. Ailisha posted those groups in a thread a week or two ago.