exaust seal ...

I bought new crush rings to seal the gap from the engine to the pipes but it seems that is a pretty big job - is there a way to seal this with out having to pull off the entire manifold?  is it possible to do one pipe at a time?  

Unless you have an aftermarket system with separate pipes, the whole header has to come loose, so you will need to replace all four gaskets. It is a little fiddly,  but one person can do it..

A little dab of grease on each gasket will hold them in place as you reattach the header.

And scotch tape (because it's thin) around the 2 inserts for each header tube to hold them as you assemble.

 

does this involve loosening removing the entire exaust system? 

I seriously doubt it, but that may depend on what exhaust system is on the bike. Typically, you just need to remove the eight nuts and the clamps. There should be enough room and flex to get the pipes out of the way far enough to remove and replace the old gaskets. Be sure to soak the nuts and studs in a good penetrating oil like Kroil or Liquid Wrench ( not WD40). The studs are small and easily buggered. Also pay close attention when removing the old gaskets, as there might be more than one at each port.

I don't think you will be able to move the downpipes without unbolting the rear exhaust hanger(s).  Don't remove the long bolt...just remove the nut and that should allow enough room to pull the pipes forward enough to get at the gaskets.

If there is a clamped joint between the collector and mid-pipe, then loosening that joint should be enough. Again, it depends on what sort of exhaust system is on the bike.