You can easily do that by putting
STR_TANK_CANNON: Tank/Cannon(need 30)
under extraStrings: in a ruleset. Problem is, then it shows up in the UFOpaedia in that manner because it uses the same string in both spots. Haven't tried to manipulate it to see if you could create separate strings for these 2 things, but I suspect not unless the code is changed, which would then affect everything else.
It'd be nice, but it really is only a problem when you first jump into the game. Once you've been playing a little while, it becomes second nature. That said, I have seen Let's Play video where this has been a problem.