I'm using Prince 10 rev 7, and my generated PDFs open in "Fit Width" magnification. Currently I have to open each generated PDF in Acrobat, and use the File > Properties > Initial View menu to set the magnification to "Fit Page", which involves manual work on each file. Is there any way to achieve this programmatically via Prince?

This is supported from Prince 12 onwards:

@prince-pdf {
    prince-pdf-open-action: zoom(fit-width);
}

For Prince 10 you can try:

@prince-pdf {
    prince-pdf-open-action: command(FitWidth);
}