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
Duplicate of MC-93200