Is there any way of programing my Harmony to default to the Navigate mode after selecting a certain activity?
EG: I select Watch PVR and my mode screen is in the Navigate mode (not the Playmode where it defaults to)

This is possible and infact how my remote is set up now...
From the Harmony site....

At the moment, we do not have a GUI for this. However, the underlying Harmony engine does support this type of customization. To change your starting mode, you need to add a StartingMode option to the activity XML.

Click on the icon for your activity
Select 'Modify the XML for this activity'
Insert the new OPTION into the OPTIONS tag. Your XML should look something like this (with the "][" symbols replaced with "><" to work with the remote, they had to be changed to show up on this site):

[CONFIGURATOR]
[OPTION]
[OPTION]
[NAME]StartingMode[/NAME]
[VALUE]ModeNavigate[/VALUE]
[/OPTION]
[/OPTIONS]
...
[/CONFIGURATOR]

Note that other possible modes include ModePlay and ModeControl
Update your Harmony

I tried changing modes using this syntax in my
"Watch Television" activity. It didn't work on navigate mode but would work on control mode.
After examining the code in one of my change button functions, I realized the activity doesn't have a navigate mode. The xml shows it as ModeInteractiveTv even though on the remote it shows it as navigate mode. Anyone know a way around this?