is it possible to force replacing items in hotbar when claiming kit? so items from kit will replace existing items in hotbar?

That would happen when plugin was originally released which led to a lot of complaints from players who did not want to lose their weapons from the hotbar but did not place them in the inventory to save them. So the developer wisely put a warning notice in the plugin which would tell you " you do not have enough space to redeem this kit" which would give the player some time to save the hotbar items without losing them.
I have a warning in my welcome message which tells players not to claim a kit with a full inventory,

If this change is added to the kit plugin i hope that it is optional .