Transfering tags from one object to another

This now exist the transfering tag feature here in the Merkaartor. (Copy/paste tags),
but it transfer all the tags.

(For example - the object has two tags, and other object has full set of 6 tags. I need to multiply just absent 4 tags, and don’t multiply existing 2 tags.)

question: How can I transfer not all the tags, but just selected set of few tags?