Most "official" load data is weak compared to what the 10mm was intended to be. I assume this is because users may have unsupported barrels and lawyers. My Para shoots Underwood without a hiccup, so I figure it can handle more than the glorified 40sw loads listed. I have the latest Speer, Hornady, and the very outdated Sierra manual. Lyman manual is on the way from Amazon, btw.

How do I approach exceeding the maximum listed loads? Should I change anything besides powder charge? Such as primers or O.A.L? I don't want to go too crazy on velocities. I just want to get closer to the full power premium factory loads.

In the pull-down section of this forum you can study exactly what was inside what was sold by the various commercial loaders.  You can copy them or adjust them to suit your needs!  Just understand that the data listed is there as a reference and documentation for people to see what they are buying, as handloaders we can understand how they get their numbers.
Be safe! 

The problem is legal departments, a huge variety of firearms and the condition of those firearms, and more than a few fools that forget the start low and work up part.

I never pay much attention to the book max.  I work up to a point where I'm pleased with a load and there is no pressure problems, push it a little farther to be positive there is a saftey margin, and back it back down to the prior load so it will be safe under all conditions.  Keep in mind that that load is safe in THAT GUN, but might be too much for a different firearm.  Much of the time its over book loadings for the given combination.

My pressure testing tool for 10mm is my stock Glock.  When I can see where the feed ramp was on a fired case, that's far enough in my humble opinion.  About half a grain less than that loading and I consider it safe, both for the Glock as well as for my two Witness pistols.  They can take quite a bit more pressure before showing any signs. 

Greg