Thanks Boyd. I tried using TYPViewer , and it works fine. I like how you can see the custom symbol as you're making it, both in text and visually. I didn't end up using the extended label option.
My workaround was to use a different symbol for higher zoom levels. For my mile markers I picked "0x0300 Large City" so that the symbol would be visible when zoomed way out, but the labels were too small.
At lower zoom levels, I picked a symbol '0x1604 Daybeacon, red'. These symbol types show up at large scales only, but what is useful is if the GPS receiver settings are changed, the labels can be set to large (or small).
In all cases the symbols were changed to custom types, but the label behavior seems to be tied to the original Garmin symbol type.
My workaround was to use a different symbol for higher zoom levels. For my mile markers I picked "0x0300 Large City" so that the symbol would be visible when zoomed way out, but the labels were too small.
At lower zoom levels, I picked a symbol '0x1604 Daybeacon, red'. These symbol types show up at large scales only, but what is useful is if the GPS receiver settings are changed, the labels can be set to large (or small).
In all cases the symbols were changed to custom types, but the label behavior seems to be tied to the original Garmin symbol type.