a) How do I work out which new licence keys relate to which old keys ?
When a license key is first assigned to you, it is "blank" (status of "re-issued") and can be used for ANY domain name. Once you use that key for the first time with snippetmaster, it becomes "locked" to the domain name you are using. From that point, it can ONLY be used with that domain name. You can transfer a license to another domain at any time by viewing the details for the license key in your Client Area (license management system) and then clicking the "re-issue" button when viewing the license key.
In the Client Area, it is a bit difficult to track what domain name belongs to what license key. My recommendation is to manually keep track of what license key you have used for each domain name. Currently, the only way to view what domain name is "assigned" to any license key is to click the details for the license key. I will eventually be adding the ability to easily search for domain names and list licenses by domain names. At the moment however, there is no easy way to do this, except to look at the license details to see the "hostname" for that license.
b) What do I do with the new licence keys?
You pick any license key (that isn't already used -- see my note above), log into Snippetmaster, click the "admin" link, and then click the "Change license key" link.. then enter the license key and save. Easy! You can also find this instruction in the documentation here:http://www.snippetmaster.com/documentation/upgrade-lite_to_pro.html
c) When I run new version I receive alert telling me that editor is being loaded....and then it just sits there.
Not sure why that was happening for some servers, but the new version I just released (version 2.2) should fix that problem.
Also, perhaps I am missing something, but if I change the snippet tags locally and upload my version of any given page, it will be an old version that will no longer carry the changes made over time by my customers ?
Well, yes... since they would be updating the file on their web server, then you'd always need to download the "latest version" to your own computer if you wanted to edit it yourself....