The header says it all. I've installed CM12.1 mod. I want to flash other ROMs now, but losing all my settings and data is not an option. I checked up on the net, but the tutorials are all about backing up stock ROMs and I'm not sure it will work on custom ROMs as well.(Bear with me,noob here).Any help would be appreciated.
Now that you mention custom ROMs, I'm sure you have a custom recovery in place as well. Eg: TWRP, Clockwork or Philz. These recoveries allow backing up data from any rom, both stock as well as custom. Provided the backup is restored to the same base. Like 4.4.4 kitkat backup works only on 4.4.4 and doesnt work on lollipop or even 4.4.2. As each base and rom uses highly customised settings to store backups, restoring backups may or may not work.
But, if you are looking to backup only apps, I'd recommend Titanium backup as it works 95% of the time irrespective of what rom you're on.