The problem with this is, that any unit harvesting the tree will "forget" which tree he is harvesting, since technically it will be removed and replaced by another. Any triggers referencing the destructable will also loose reference of it.
Indeed, but have you tried this method about the harvest problem? considering the nature of harvest itself, won't the unit just resume the order by looking for nearby/adjacent tree?
about the trigger problem, yes, that's why I recommend this method if the destructable isn't used with hashtable or cache, maybe I should use word "trigger" for wider meaning. of course another workaround for that trigger problem will be readjust the trigger upon replacement. other than that, for now there is no option to rescale destructable,
or
you can use Daffa the Mage's method
by using dummy unit, but don't add Locust, just
change the ownership to neutral passive,
disable movement and attack, then
set combat - targeted as tree and
add classification tree.
the downside will be the tree is clickable and probably has armor or other unit trait.