Selecting proper vales of Rb, Re and and Rbe in a NPN transistor emitter follower configuration?
No, your solution will affect normal transmission. When the collector of the transistor is driven low (while the "break" signal is high), the "break" signal will drive current through the two 1K resistors and the B-E junction of the transistor, holding the output (the emitter) at almost Vcc/2.

What you really want is an ordinary AND gate. When both inputs are high, the output is high, but if either input goes low, then the output goes low. Note that you can purchase single gates in SOT23 packages for applications like this. Look for the NC7SZ family from Fairchild, or the MC74VHC1GT family from OnSemi. This would be the preferred solution.

Since you asked, you can make an AND gate out of diodes, too (just reverse them from the OR configuration and use a pullup instead of a pulldown as a load). You could even use one of your NPN transistors as a dual diode. Also, you could use a second NPN transistor as an emitter-follower buffer, which would cancel out the level shift caused by the diodes. See below: