How to connect/disconnect signal line electronically?
This is probably not the best way to do this, as the voltage will drop 0.6V across the transistor (assuming its saturated, which it's probably close). For 3.3V TTL the Vih is 2.4V or 2.0V depending on what you have, so odds are you'll still turn on the logic your connecting to. But this isn't the way to do this.

There are better options. 

A TLL buffer with an enable line would probably be the best: 


Source: https://www.allaboutcircuits.com/textbook/digital/chpt-3/special-output-gates/

There are lots of chips available if you search a distributor (like digikey) 

Another way would to use a switch with a low resistance: 



The low resistance keeps the voltage from dropping.