The Variations Service Intro only allows for creating a new variation from scratch, with a few of the most popular options.
The remaining Variation Service pages work much like the Intro, except that they create a new variation based off an existing variation that you already have, and that they offer more options. While the existing variation (which may be one of the Standard Variations) is running, use the ‘P’ command of the Mini vMac Control Mode (type Control-P, usually) to copy to the clipboard (of the real computer, not the emulated computer) a string containing the options describing this variation of Mini vMac. (They are defined in the “Options” documentation.) Paste this option string into the first field of one of these pages:
The most popular options
Many more options
To specify changed options with text