Can I use words like hereafter, therewith, whenceforward, hereinbefore, therebetween, etc.?
You evidently can, but it may not be your best interest, thenceforwardly speaking.
What if I rephrase my original question to “May I use such words like mentioned above?”
Of course you may.
But doing so might be a bad idea.
Thanks, I have decided I will not use them unless absolutely necessary.