[dtengineering]

With the exception of the motors, batteries and electronic bits I haven't seen any rules to the contrary (so go for it). Modifying (sometimes heavily modifying) structural and mechanical components is a bit part of FTC and VEX style competitions. Indeed in FRC you can go even further than in VEX or FTC as there is no restriction against welding the Tetrix parts together. (Check alloy composition and tempering before breaking out the TIG, or at least try a few tests on disposable bits, though.)

Jason