[Xposed General] AllTernative:
I actually saw that, but I wasn't able to find a modified version which does not look fishy. So I tried a random version I found on the Internet and the one from the Appstore to no avail. If you could point me in the right direction or send the link to the apk you used I'd be very grateful.

//edit:

I got one of those fishy Titanium Backup for Bluestacks apks and installed it. Same problem. Then I checked with a file explorer for root access and there is none. So I suppose the Bluestacks version isn't fully rooted? I'm going bananas here.

//edit2:

I installed a kingroot apk I found on the Internet and applied root with it. Somehow the Titanium Backup 7.5.0 for Bluestacks seems to work. I managed to take a backup but now my Bluestacks crashed and cannot be opened again. I will try to reinstall it completely and report back.

//edit3:

Well, I finally got it working - no kidding. Although it was a pain in the ass I'm glad I've done it. For everybody fighting the same fight with Bluestacks, I'll try to guess what got it working:

-I (re-)installed Bluestacks 2.5.55 from this link, the newest, pre-rooted version (although it doesn't seem to be pre-rooted) http://xdaforums.com/wiki/BlueStacks_App_Player

-installed Snapchat from the Playstore in Bluestacks and log in, then close it

-installed Titanium Backup 7.5 for Bluestacks (you will find it when querying this in google, not sure if it works with other versions)

-noticed Titanium Backup freezes on "Detecting SU and Busybox" - close it

-install Busybox App from Playstore and install Busybox inside the app - I did the normal install, not the smart one

-install SuperSU from Playstore, open it and notice the message saying to update SU binaries - just ignore it and close SuperSU

-google for Kingroot apk and install it (unfortunately I cannot say where I got it from) - when you do not install SuperSU kingroot will display it doesn't recognize your device/root method

-swipe the Kingroot screens up until Kingroot displays a centered button to root - hit the button and wait

-when it's done Kingroot will display you're succesfully rooted - close kingroot now

-open Titanium Backup again - it will now skip the previously frozen screen and work

-do a backup of Snapchat

-once it's done download a file explorer (I recommend FX Explorer) and navigate to the backup folder (it's most likely "TitaniumBackup" on the internal storage)

-copy the 3 files to your phone (I copied them in FX Explorer to internal memory -> windows - a mounted windows users folder - then transfered the files with Airdroid to my phone)

-open Titanium Backup on your phone and restore the backup (app + data)

-for me it didn't work by now - when I opened Snapchat I was logged out - so I opened Titanium Backup again and restored only data (it will ask if it's okay to kill the running snapchat app, confirm this)

-I am now logged into Snapchat on my phone again

Some hints:

You do not need Titanium Backup Pro for this, the regular version works just as fine.

This can also be done inside a VM, although the performance was pretty bad and kept me waiting quite some time.

I had Snapchat deinstalled on my phone before restoring the backup.

There might be an easier way to do this, but this was the only one that worked for me.