All the Mamiya C TLRs have a lens change baffle controlled by the lock/unlock control.

http://www.btinternet.com/~g.a.patterson/c330/c330.html has a picture of the inside with the baffle up and down.

By Tony McGartland on Sunday, December 21, 2003 - 07:56 am:

I am purchasing a C330s TLR in mint condition. However the seller tells me...... "it appears not to have a slide to enable you to change
lenses in mid use,this feature must be on much later models". Is this in fact true, I thouhgt all C330s models were similar.