In case anyone else needs this info - I couldn't find it on the internet.
Now that W204s are 15 years old they can be easily imported to Canada.
I got one and I don't use the COMAND for much of anything since it has an aftermarket Android Auto box installed for nav and everything.
One issue is that the Android box doesn't seem to have an FM tuner (maybe some do?) and the COMAND FM radio only picks up the Japanese frequency range 76-90 MHz (some Japanese cars have 76-95 MHz).
The dealership offered to install a new NA head unit for $3000. Um naw.
A wrecker offered to sell me an NA head unit for $500 but as-is with no help coding it if it needs it which he said it would and no returns. I passed.

After a lot of googling, you can change the region for your COMAND (head unit) to NA in the engineering menu, but there are some caveats.
You could find yourself with a non-functional COMAND.
Some people have found the COMAND software just starts crashing and bootlooping if you make changes like this. I did experience this after one change but luckily I was able to get out of it.
You might find after making this change you can't get back into the engineering menu to undo it. I thought I was in this position but I found a way to get back in.
After this change some features are a bit messed up - mostly functional but some buttons have no labels - so you have to "just know" what they do.
This doesn't bother me because as I say, I only use the COMAND to tune the FM radio now - literally nothing else.

So if you want to risk it here we go:
As you can easily find out all over the internet, you can get into the Engineering Menu by holding HANGUP+POUND+ONE keys simultaneously.
Once in, go to page 7. HW SETTING and 7.3 MARKET/DVD SETTING and change (1) ECE/US/JAPAN to US.
Then go back to main and choose 9. SYSTEM RESET
System will reboot in US mode.
This killed the NAV feature for me which I'm bit sad about because it's kind of fun to switch to it sometimes and see myself driving around the outskirts of Tokyo (the NAV in confused and thinks it's still in Japan) but I can certainly live without it.
What I found was that I can now go to AUDIO in the top bar and when selecting audio input, the FM option is now replaced with a new menu option that has no name. You can still select it like normal. This is the option for the NA FM tuner.
The tuner works fine for the most part except that when using it, the bottom bar buttons have no text.
You can still click them, the left most one is settings. It brings up a settings menu with two blank options. One turns RDS on and off and I forget what the other one was but something obvious.
There is a blank button to bring up the preset/scan menu which works fine.
There are a couple more blank buttons which simply don't work - pressing them freezes the radio tuner screen but you can easily unfreeze it by switching to SETTINGS and then back to AUDIO.
Not sure what those buttons were but I'm not missing them.
The rightmost button goes partly off the screen because the blank buttons are of a standard width which is too wide to fit on screen but its the audio bass/treble/balance settings.
I thought well if the firmware is missing localization for those button label strings, maybe I can switch the language to Japanese in settings for a moment in order to see them and use google translate.
So I went to COMAND settings and pulled up the language menu, but all the language names in the selection menu were blank.
So I thought since the first blank option was currently selected and was obviously English, I'd try the second option whatever is so I selected it, and then the system rebooted.
My dashboard switched to French and the COMAND booted up but then immediately started crashing and rebooting every three seconds HOLY $#!& I just ruined it!
Luckily that three seconds before it crashes was JUST long enough to get into that menu and switch back to the first option (English) and the crashing stopped.
At this point I thought I go to the engineering menu and switch my market setting to Japanese for a sec (because Japanese market with English language does give me readable buttons in the radio)...
...but the HANGUP+POUND+ONE combo no longer works! HOLY $#!& I hope I never need it again.
But then I thought about the fact that Japanese PlayStations have the action and cancel buttons backwards from North American ones so I tried CALL+POUND+ONE and you know what? It worked.

I noticed there is an option in there to turn NAV on HW SETTINGS - it got turned off when I switched to NA - but there's a real risk of bricking this thing if it tries to access the NAV and finds that it's not the software it's expecting, just like when I tried to change the language - so I'm not going to risk it.
In fact I'm not even going to risk touching anything again. I've got NA radio frequencies and that's all I wanted.
(Although if my AUX input had gotten turned off in the change I would obviously risk turning that back on since the Android box need to have AUX enabled for it to work).

Alright there it is. Try at your own risk obviously. If this bricks your COMAND sorry about that you'll probably need to just get a new one.