You're right that the loads imposed by a spinnaker pole are likely to exceed those of the radome. The track pictured looks like the extruded form (ie part of the mast section itself rather than bolted on) which should be plenty strong enough. Finding fittings to match the extrusion and lock in place securely might be tough to find, and of course you'll need to do some adapting to the mount of the radome itself.
As far as adjustability goes, I doubt the difference of a few feet here or there is going to make a huge difference to the usability of the radar unit.
I think you'll get differences in performance if you can vary the height of the radar from say, 20 feet above water to 30+, but being able to slide it up or down 5-10 feet may not make a substantial difference.
Finally, how are you going to handle the cable entry? If you want the adjustability then you're going to end up with extra cable exposed, depending on where the unit is set. Even if you just want to find the "sweet spot" for a permanent fixture, that's where the cable entry should be in the first place... and to prove all this you'll need to have the unit powered up and operating....
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)