There is only a slight confusion here. BaseCamp has Activity Profiles, these allow you to set what Map Display Features you wish to see on whatever map you are using in Basecamp (irrelevant to the Montana), and more importantly, what routing options you want, i.e. faster time, avoidances, etc.
The Montana uses Profiles for much more, like setting which map to use, how you want your dashboard or menus to look like, and dozens of other custom settings.
The key here is to set the activity profile in BC to match the same activity as part of a Profile on the Montana: (setup>routing>activity...calculation...avoidances, i.e. automobile driving, faster time, avoid U-turns.
This, along with identical maps on both, will give you the best chance of having your carefully tweaked route in BC function the same on the Montana without recalculation.
Nothing you do with Activity Profiles on BC will change Profiles, default or otherwise, on the Montana, except that you may have introduced the possibility of a mismatch in Routing Activity. This is only true for autorouting, if you are using direct routing and topo maps on the Montana none of this applies.