I assume this is not what they will do. Clearing the forest means to find hidden stuff. Some goods or whatever. You can find crowns under trees or by exploring ruins. Speed ups is ok, but this you would not find if you are exploring the deep rain forest
you will find ruins, buildings, troops and so on.
the problem is, that you cannot move the merc and you cannot replace one merc by another like you do with generals or normal troops. You need to use them by throwing your active mercs away. And that’s the reason why this topic exists.
TheWise to replace one single merc would also solve some issues. Can you check it out if you can add a button inside the dialog of the mercs to delete one single merc for replacing them by another one without replacing everything?