The graphite-epoxy material itself will not change over time. The stress you put it through in normal use is well within its elastic limit. And GrEp is a brittle material, so it will shatter about the time you exceed that limit. If you're using other, stiffer rods, it might seem like it's changing when it really isn't.
But Loomis can, and does, change both the material and the design. The material in yours is probably several generations behind what they're using now, so if you have other GLX's they may flex differently.
And you CAN get a change in how the ferrules behave. They can loosen up over time, and it's especially noticeable in a 4-pc rod (if yours is that old, it's probably 2-piece, right? We didn't realize we all "needed" 4-piece rods back in the 90's)

Try some ferrule wax and see if that helps.