Let's say that we have an existing Magento store in 1.9.1
This is a live store with customer accounts and purchases, categories, products etc. etc.
This is using a certain template (which is crap)
Let's say i want to create a new look using the rwd theme as starting point.
Is it (when finished) just a matter of moving the new "theme" files to the correct app and skin folders of the live site and will that have no effect on contents etc. (i guess that's all in dbase while these are just files)
And is it the same when i want to update to new version of Magento?