Submit a put transaction for the entity with the document at tx0 but with the valid-time of tx1
Depending on the exact semantics you need, you may also want to add an end-valid-time parameter to your put ops also, especially if there are later entries in the history that have been affected too.
The strategy sounds about right though 
I’ve seen “decant” mentioned in a couple of different posts on this forum, but see no references to it in the docs
My fault, sorry, the term has been picked up by osmosis from the Datomic community (e.g. here) but it has a fairly casual meaning as far as I’m aware. Probably is something writing up formally somewhere though 
In any case, the description I gave previously (for v1) stands: Shrinking the Database.