My new company wants to clean up their SFDC campaign types so that it's a small, easily understood list ("Event" instead of "Roadshow," "Tradeshow," "Happy Hour," etc). Most of those more detailed values are coming from several marketo program channels that are syncing over. What would happen if I change those values in SFDC? Will the sync break, will Marketo re-write the program channel value, or will Marketo ignore it and let me keep the new value in SFDC?
SFDC wont let you remove program status values if leads are already assigned to those statuses. Also typically for a program level sync you need the program statuses and the SFDC campaign statuses to line up. I've seen it where SFDC pushes some crazy different values and changes what was in Marketo.
If they want to consolidate the statuses in SFDC you'll need to evaluate your Marketo program statuses and see if they align with your overall goals for each program. Or you could just sync the program in a flow step(which is slow if there are a lot of leads).
I'd recommend first to get your channels set up to your marketing efforts. So go through the list and decide what the different ways are that you market to and bring in leads, and with that make sure the statuses make sense.
Then we'd recommend creating a SFDC campaign type for each of these channel types. This way you can create the SFDC campaigns either way (through SFDC or MKTO) and have the statuses align. Ultimately you want to make sure you have statuses aligned with successes so you get some credit for responses in SFDC reports
Before you change any SFDC Campaign Types, I would create a field mapping worksheet. You don't want to lose any campaign data that you have accumulated, so you want to map your old Campaign Type values to the New Values that you want to create. Then create your Marketo channels and tags to match your SFDC Campaign types and Campaign Member Status'. I have learned that in order to use the Marketo/SFDC campaign sync feature that these values must be in complete alignment or the campaign sync feature will fail.
I agree with all of the posts above on best practices around aligning your Channels and Campaign Types. However, to answer your question directly, if you change a SFDC Campaign "Type" and it no longer matches the Marketo Program "Channel", any existing Programs synced to Campaigns will still continue to sync. The important factor that must stay consistent are the Program Statuses - Campaign Statuses. To others points, if those are not in alignment, the sync will break.