Can someone tell me, if I have now set my site up in one particular skin, can I swap at any time to another without any problems or will it simply take me back to a fresh new site that I have to add modifications etc to again? 
I have not done this, but logic dictates that any ātemplateā changes would not appear if you changed skins.
I may be wrong, so this is not gospel
Thanks Mike, even 6 months on CS still scares me!
Mike is correct - most changes made in one skinās TPLs need to be recreated if you change skins. There may be exceptions for some TPLs in the Base skin which appears to include TPLs which are common across multiple skins (e.g., breadcrumbs.tpl or fileuploader.tpl in /common_templates).
Bob
If you change from a āmodified skinā to another āunmodified skinā and then back again your modifications will still be there.