I’ve updated the rout.class.php in 1.5.X branch (dev-branch)
I will ask @MarkG if you would like to install this to see if it address what you need directly?
I know you don’t want to move to the alpha build, but dev-branch is where the bug fixes found since 1.5.5 have been addressed.
If anything, you can simply copy this dev-branches router class with:
wget -O /var/www/fog/lib/router/route.class.php https://raw.githubusercontent.com/FOGProject/fogproject/489ba2952f5750e1483083eedade17dde6bb3cd8/packages/web/lib/router/route.class.php
This should allow you to clear out items such as snapins with the code you were using:
{
"snapins": [],
"printers": [1,2,3,4]
}