There are plenty of persistent windows commands, issuing them once is sufficient.

setx is just editing system environment variables. Go to System Properties > Advanced > Environment Variables > User Variables

There's your 2 parameters.

So doubt or not, it works 

P2P (P2Pool.cachecoin.org) has been extremely stable for me, maybe it's your latency to the node? 1-2% rejects on 280x. 4.5% rejects on my 290's

I solo mine once hash drops back below 100MH/s.

Either way, good luck mining!