You could download an old version of the SWS extensions at
http://sws-extension.org/download/old/ and hope these actions are already implemented. Alas, I don't know which version was the last to support Reaper v4.x.
Do you know that if you paid for Reaper v4.x then you are eligible to use Reaper up to version v 5.99?
As of MIDI FX, I simply mean FX plugins (VST or JS) which process the MIDI stream. For example I believe there's a JS plugin called something like MIDI Tools can switch the MIDI channel, or you can very likely find one for the job at
http://thepiz.org/plugins/?p=pizmidi. But I don't remember whether Reaper v4 already had input FX chains in the first place.
Regarding the track-per-channel method, it doesn't need multiple instances of your multi-channel instrument. You need one track with the instrument plugin and then tracks for each of the MIDI channels you want to use. From each of the "MIDI tracks" create a send to the instrument track. Then you setup each send to change the MIDI channel on the way through.
For example on the channel-2-track you'd set
Audio [None], MIDI [All]->[2]
That way you record the MIDI on whichever channel your controller spits out and on the way via the sends to the receiving instrument the channel is mapped to the one each track is supposed to trigger.
One aspect I like about this method is that you can paste any MIDI onto one of the tracks (say a line from a flute track onto a viola track) and it will immediately trigger the appropriate instrument without need to care about editing the MIDI channel.