If you set a chain cmd to conditional, place the one before so that it powers the first one from the side it will completely ignore the command in it.

Example: 1.(pointing to the 2 from the side) /testfor @p[m=0]

{Unconditional, Always active, Repeat cmd}

2. /say hi

{Conditional, Always Active, Chain cmd}

Power the repeat cmd.

Result: no text with "hi" in chat