exchanging the model won't work for furniture, since furniture markers are part of the model.
there's still things you can do though.
like:
select your object window's furniture-section, filter to "marker". you'll get a lot of invisible furniture stuff, bed seats etc.
put one of these over the static (your haypile or whatever), add an activator with a script going like
Event OnActivate ( ObjectReference akActionRef ) if GetLinkedRef () GetLinkedRef ().Activate ( akActionRef, true ) endifendEvent
and make the invisible furniture a linked ref to that activator.
that activator can either be a triggerbox (don't forget to check "player activation" in ref's primitive tab and giving the base object a name, so you'll get an activation prompt)
or that haypile itself, made into an activator (THIS can be done with the model exchanging method)
(or if you don't need it usable for player, but npc's only, you'd not need an activator at all, npc's use furniture markers without one)
or another thing you could do in some cases, you can take the original furniture and make it invisible by retexturing it all with "nullTextureSet" - this will NOT disable their collision though, so it'll only be applicable where shapes at least roughly fit (like, for alchemy and enchanting, there's "tabletop" versions, they're pretty flat, so stg like this might work with models like that)