I have a spare Lumia 521 that I want to try the preview on. If I switch My SIM over to the spare and download the preview will it mess up my MSFT Acct or primary handset if I switch SIM back to the primary. Thanks.
Beat me to it, Harrie/Xandros. BTW...its great that you always mention knowing how to use the Recovery Tool. So important!No it will not but you do not need to put a SIM in your 521 to download the preview.
Furthermore you could create a new MS account for the 521 so then really nothing can happen.
Good luck
And please first download the WPRT because you need it to roll back to WP8.1