Do you mean Stage Pianos or Home Pianos or 88 Key Workstations or 88 Key Performance Synths?
It will depend entirely on the make and model and category of keyboard you purchase.
Some have zero tweakability or expandability.
Others have limited abilities to load and run new patches with effects and voicing tweaks but not actual samples of new instruments.
Then there's some of the better class workstations which can load new patches and new samples for completely different voicings.
Be more specific if you are looking at a couple of particular models and we can tell you what sort of expansion capabilities they have.
Gary
