I'm going back a good few years but having bought an f-14 I thought one of the benifits was it was so modular. Wasn't that long one of the mags showed how to do dual rates -so I did that on the f-14 for a few just quid compared to the full price switch. f-14 had extra unused channels built-in so I made my own switch banks which co-incided with veroboard positions.
So still have my F14 and is still my favourite transmitter to hold in my hands, ever. Whilst I can't remember the diy mods I did on it it wasn't rockt science and I think same technology gave maybe 10 switched functions from one channel like MRW or others offer for decoders. I never did quite work out what 70'odd quid bought for a couple of switches and resistors on a board got, plus a 60'odd quiid expander module achieved when there was a 40odd quid expander decoder and tx mods were between 5 and 10 quid.
...Unless of course I guess you wanted to finesse and ultimately push the F series upto and past 20 channels. The number of functions at that must be enormous.