@mitu i'm on 4.7.14 retropie image now. everything is working. if the drivers dont work again when a new upgrade is released, i'll just have to install an older driver again. not a big deal. just glad its working.
Sure. You want to handle 2 video configurations - output to HDMI (which is default) and via the LCD. Save the default config.txt in /boot/ as /boot/config-hdmi.txt. Install and configure the LCD drivers (modify the config.txt) accordingly, make sure it works, then copy the config.txt to /boot/config-waveshare.txt.
Create 2 scripts in /home/pi/RetroPie/retropiemenu
cp -f /boot/config-hdmi.txt /boot/config.txt
cp -f /boot/config-waveshare.txt /boot/config.txt
make the scripts executable by running
chmod +x /home/pi/RetroPie/retropiemenu/hdmi.sh
chmod +x /home/pi/RetroPie/retropiemenu/lcd.sh
Now, when starting EmulationStation, you'll have 2 new entries in the RetroPie system - HDMI and LCD, executing one of them will switch the video output configuration. After running one of the entries, you'll have to reboot to activate the new configuration.