Only the old 2x2 and 2x4 non powered multiswitches degraded the signal and then not enough to worry about except in extreme conditions.
Current 4(5)x8 multswitches are POWERED and have a small amp to compensate for the insertion loss.
Normally about 7DB or so.
You should not worry about adding such a switch.
Due to the digital nature of the signalm as long as you a a miniscul amount stranger than what is required to decode the signal, then even the strongest signal will appear identical.
Why we strive for best EcbNo and signal strenth are on those occasion were the signal becomes naturally attenuated by weather and such.
The difference between what you have and when it drops the signal is often called rain fade margin.