when it's on your level 50 the rested bonus wouldn't be used so that part should be good.

But I do want this use rested bonus on/off feature...

I want to use on my main crafting class say Armorer lv45 but to get some mats I would go change to say Miner lv35 but I don't want exp bonus to be on it so having rest bonus on/off feature would help in these type of situations.