Backup/restore question for Moto G XT1033 converted to XT1032 GPE I have installed TWRP as my recovery and rooted my device. But I only had the space to backup the "system" and not the "data". Now I was going to install CyanogenMod. 

My real question is, if things go south during installation, will I be able to return to system with Phone (sim) and Play Store apps working through the "system" backup?
Moto G XT1033 as it seems from this question supports OTG, which means you can connect a pendrive using an OTG cable and store complete Nandroid backup in it through the recovery.


  Will I be able to return to system with Phone (sim) and Play Store apps working through the "system" backup?


I cannot comment anything about Baseband/IMEI issue, but you will definitely lose Play Store apps since they are downloaded and their data stored under /data, which you're not backing up here.

On a side note, the device has good amount of Internal Storage available; can you not make space enough to store the backup in it?

May be you can try making a backup of /system only and then pushing it through ADB into the PC. Do the same for /data and /boot now. ADB will work in Recovery.