This would normally be done by writing a batch file to do this for you, however I have managed to find a piece of freeware, process master (64.2kb freeware, malware free), that will do this for you in a GUI, and will start with Windows. Basically it puts everything at its standard setting untill it is used, and is then promoted to higher status,

It can work in reverse by putting processes to lower priority too. There is an option for it to start with Windows should you so desire

Note: I do not recommend that you "demote" certain key processes, such as svchost.exe etc