TL

R? Yes, it can be done with non-ICS parts but it's probably not worth doing at all.
To explain:
I have three ICS guns - two of which definitely fit 'standard' AEG rails/outer barrels. The third is a much older ICS gun and I haven't tested the barrel threads but I assume that will be OK too.
I would not be swapping the barrels/rails over on the existing upper receiver on a regular basis - unscrewing and re-screwing the barrel nut and rail will eventually knacker something - most airsoft guns (Including ICS M4s) are only made from relatively soft Zamak metal. Buying a replacement
MARS upper and building a complete short front-end off that instead would be a more sensible approach, because it would only be the matter of pulling the receiver pins and swapping the upper before game day.
Problem is - you could end up spending a fair bit of cash buying an upper receiver, rail system, inner and outer barrel. You might need to think about another hop unit/rubber/nub because you don't want to be swapping that over between your inner barrels. Then there's the problem with volume-matching cylinders between the different barrel lengths if you choose to go really short, so a new upper gearbox might be needed too. Overall, you could be looking at well over £100.
Frankly, you might be better off buying another gun altogether.
I did this by buying an ICS CXP-15 to complement my longer guns. You can get a plastic one for
£130 brand new. I run mine with a
stock adapter and
Stubby stock and it's brilliant in CQB. You could run it as a straight-up pistol just attaching a sling on the back and that works extremely well too.
Another thing - and you might not like me saying this - is that your gun is already pretty short, well within CQB norms. If you struggle with the length of it (ooh err), it could be a gunfighting technique issue. Perhaps look at attachments that will help better control what you already have (e.g vertical grip) and try to remove as much unnecessary weight from it as you can (you don't need gucci red dots with magnifiers etc.)
Just my 2 pence.