Is there a way to remap Command-B so it changes the character style to my Emphasis style?

I'm building a custom template where Helvetica Neue Light is the primary body text font, but going from Helvetica Neue Light to Helvetica Neue Bold is far too large a contrast for my tastes. So in this template, I set the Emphasis character style to Helvetica Neue Medium.

I've already mapped that style to F7, but it's a pain in the butt having to hit Fn-F7 whenever I want to make text bold, rather than just using Command-B as I've been used to doing for 20+ years now. I'd like to be able to press Command-B and have my Helvetica Neue Light text turn into Helvetica Neue Medium.

Is there a way to remap Command-B so that it changes the character style on my text to Emphasis, rather than using the Bold option on the font itself? (I wasn't able to set Command-B to change character styles through the Keyboard options in OS X Preferences, since individual character styles aren't in Pages' dropdown menus.)

Or, alternatively, is there a way to change the preferences for that specific font—either in that specific template, in Pages, or systemwide—so that when Helvetica Neue Light is in use, making the text boldface uses the medium-weight version of the font rather than the heavier bold version?