Is there a way to take a duplicated output and adjust the phase and pitch of it?

Chorus uses a delay line to implement a pitch shift that gives the effect of two or more voices... the implementation causes audible artefacts that give it it's characteristic recognisable 'sound'.

The reason these FX are a thing is because what you are asking isn't possible without some sort of audible artefacts. You could implement a traditional chorus or flanger or phaser. Or you could try a more modern pitch shifter type of approach maybe using FFT or some granular, but whatever you do it will have some recognisable characteristic of that approach.

You really can't make an 'effect' that sounds exactly as though you are using twice as many oscillators to implement unison.

There are approaches that work well in very specific situations, like using a wavefolder type approach to 'multiply' saw waves... works great for saw and sounds very much like unison, but only with saw waves - not going to be the same when applied to FM based sounds.

There are probably other tricks that work well in other limited situations. But I think if you are doing FM stuff and you want it to sound exactly like multi voice unison, with no artefacts or 'colour', then you need to implement it by adding more oscillators. Shouldn't be too bad though, FM is fairly cheap. Reaktor has a built in unison feature which might help in terms of cpu

Stacking oscillators in unison (detuned otherwise there's no point), will always reduce clarity. That's kinda the point, thicken up the sound add texture...

Its somewhat confusing... the distinction between oscillators and operators. One way to look at it is that an FM oscillator might contain multiple operators... or maybe better to call is a voice...

It shouldn't effect the operation of the FM process, you would have the whole FM 'voice' repeated, so if it's a 4op voice, you repeat all 4 operators as a block. Not the individual operators... So the FM between the operators within the voice will not be effected.

Easiest option would be to use Reaktor's built-in Unison feature. That should just automatically work assuming the Synth works :)

So I decided to give this a go using a frequency tracked single cycle waveform record and playback system, I got some pretty good results.

Here...

There are three snapshots in the ensemble.

Snap 1, no arp, playing individual notes sounds great, like true unison.

Snap 2, with arp, gets some artifacts/pops/clicks, it doesn't like rapid pitch changes.

Snap 3, Arp with glide, lots of artifacts/pops/clicks, it hates constant pitch changes.

If anyone's got any ideas on how to eliminate the problems with constant rapid pitch changes, please, let me know.

Feel free to use this for your synth if it fits your needs.