I don't have your remote, but I did try this with a Comcast remote, which has both channel lock and cable setup lock. Both features were enabled. I assigned 00174 to PIP On/Off using 11758 on TV, and used your post #5 to assign 00174 using TV as the From device and CBL as the To device, to the PIP On/Off button and to the number 1 button. TV with PIP On/Off and CBL with PIP On/Off or button 1 all shot NEC1 device 4, EFC 00174, as expected.
In CBL mode, the CBL button lights when sending these signals, even though a TV-based EFC has been assigned. So please try the steps in post #5 again, making sure that the remote blinks twice after you tap the Video Source button. This indicates that the remote has accepted your programming. If the resulting signal doesn't work, try a different button besides Video Source.