Blocked Field Override?

I don't believe there's a way to override a blocked field. It's more of an on and off option, with no exceptions. 

Our company had to make this decision also. Though in theory there should only be one source that stays the same, our processes required the source to change in order to fit our current lead lifecycle management reporting in SFDC and Marketo.

We opted unblock the field, but in a perfect world, I would rather keep it blocked and find a way to manage multiple sources as a way to report on multi-touch attribution. 

JK

You can choose what specific actions can update the field:



If you allow only "Flow change data value" then you'll be able to change it within smart campaigns, but not from list imports and form fillouts.

Yeah, we run into this issue on occasion, and the only good solution for us, unfortunately, is to turn off the blocking of field updates via flow change data values, make all the lead source updates we need to via smart list flow actions, and then turn the blocking back on. It'd be ideal if the options Steven mentions above could discern between triggered flow change data values and one-time batch changes.  

Depending on how drastic the lead source change needs to be, it's sometimes beneficial to create a second Lead Source field for additionlal information.  If what you're doing is considered multi-touch attribution, that may be something to consider, as well.

Jenn makes a good point: the best business approach here (using just lead fields) is to have a first touch lead source and a last touch lead source.  Marketo encourages this with the "original source type" field, but it never seemed to get adopted by companeis used to the SFDC standard lead source field.