Squelching is nice to have in FM mode, but it doesn't really work for SSB, where you will be looking for weak signals. Therefore you have to adjust the squelch level every time you change mode. Furthermore I enjoy using FM as a monitoring mode on the SSB calling frequency, so changing the mode happens quite often.
The solution is quite simple. Just cut the connection to the SSB input of the squelch circuit in some way.
The easiest way to break the connection is to connect the base of Q7 to ground. The base is the lead facing into the centre of the PCB.