My Fabia vrs came without a cd changer so I bought a Sony cdxt69 changer and adaptor from halfrauds and all was well.

Now though I'm thinking of upgrading the HU but keeping the cd changer.

Is this possible?

i think you should be fine as you can get aftermarker adapters for different makes of changers and stereos. e.g. pioneer to JVC, etc.

if it was a skoda cd changer you would be stuck as there is not compatibilty.