It is totally possible to convert between them easily. In fact, it is especially easy to convert backwards.
Whenever it says 1AP or 2AP read "half action" and whenever it says 3AP or 4AP read as "full action."
For weapons rate of fire it is slightly more complicated, but not much. Mostly you just take whatever they gave you and slap down double that number as the full auto RoF, that number as the semi-auto, and if a weapon has 1/2 give it s/2/- and if it has single shot it is s/-/-. A simple compatibility pdf armoury release would do the trick and nicely shove everything into one list to boot. Once you have changed the RoF listings you can safely ignore stuff about spending variable AP in the combat chapter and you are pretty much good to go.
That seems to easy you say? The AP system assumes higher possible rates of fire by basically trading away all of your reactions and making a full action attack. But the weapons' RoF tends to be balanced around not doing that since you miss a lot and want to aim (or take cover, or dodge) instead.
Other than that it really is that simple. All AP are is quarter actions. It is further granulation. Dividing each round into four pieces instead of two (two half actions / turn). Reactions became a use for saved AP and rate of fire was made to interact with it, both easily reversed if desired.
It is harder to convert forward, but not impossible. So if you love it, you can keep it. If you hate it, you can skip it. The effort is minimal. With some clear sidebars/optional rules/support documents they could go either way on this one.
I much prefer the coherence and tactical choice of AP, but I get not wanting to fight with it and I hope they can find a way to make everybody reasonably happy.