Can I pour cans into a keg? Can I pour cans of  Carling  in to a keg to use with a beer tap?

It's a 9 liter keg, and all the beer will be drunk that day/night

What gas pressure would I need? (If it's possible.) 

Can the same be done with dark fruit cider? Again, it will all be drunk on the same day/night. (It's just a show off thing for the beer garden.)

I will pour the cans in slowly taking my time, I would just like to know if it will be possible.
I have done this with homebrew beer, but never commercially-bottled beer. The issues should be the same, though:


You will significantly shorten the beer's lifespan due to the oxygenation, but if you fill the keg as full as you can so there's little to no airspace at the top and you're drinking it all that day, you'll be fine.
When you force-carbonate after sealing the keg, I'd recommend 10-15 psi of pressure.
I have no experience with ciders, so I'll defer to someone else on that, although I can't see why it would be any different.