The custom map I use doesn't play nice with the version 8+ firmware after themes were introduced. It looks like if I want to keep using it I'm will need to move most of my line formatting from TYP file to a custom theme. I found some information on editing themes for nuvi units but the format for fitness devices is different, so the scale / border thickness control option works.
If anyone from Garmin is listening can you provide a breakdown of the supported formatted options for themes along with the style field names for all features? Maybe the kmff format has an xsd defining acceptable input. Also is it possible to specify formatting for a polygon / line feature using its hexadecimal id? That would be useful for custom lines greater than 0x0C which start getting colorful names like CUSTOMIZABLE_ROUTE_LINE_1 where the mapping to id is not obvious. Even a more advanced sample theme that utilizes every feature would be helpful.