if its really a varicap + digital potentiometer I wouldnt even bother with reverse engineering software, just whack attiny in there and additional button that forces full bandwidth (I assume they use this design so you can limit bandwidth to cut aliasing, so no point hard modding to 100MHz).
that LA also looks doable, just need fpga + memory + 2 stabilizers, and a dump from someone who performed firmware upgrade (again assuming firmware upgrade also upgrades fpga firmware)
lovely compact design at a great price point, bug thumbs up to rigol (unlike their shitty still broken power supplies)