As a previous sonar Platinum owner, How do I get Rapture dimension pro Addictive Drums etc over to a new computer if I use bandlabs cakewalk

No need to uninstall Platinum, and assuming you have Bandlab Cakewalk scan the directory Dimension Pro and AD2 are in, it will find them just like SPLAT.  Also, Command Center still works fine.

I recently installed Splat and the rest of my content from the CCC to my new StudioCat.
That's step one, then install CbB; piece of cake as they say...
 
T

Addictive Drums can be installed seperately and using it's own CD-key.
Also I've used Cakewalk Command center to install some Cakewalk stuff. It is working in Cakewalk.

Yes, AD2 has its own installer and XLN tracks the number of activations and limits each license to two computers. The same is true with Celemony and Melodyne. The other two synths mentioned in the OP may be installed without Platinum. Some the "etc" is another story.
 
The best solution to get all the Platinum content installed and working is install Platinum. Using the Command Center is the easiest way especially if the installers were saved. If the installers are on the old machine (by default they would be in C:\ProgramData\Cakewalk\Command Center\Downloads) or backed-up, after installing the Command Center on the new machine copy the installers into C:\ProgramData\Cakewalk\Command Center\Downloads. This will eliminate the need to download everything. Grab the XLN installer and Melodyne from their manufacturers. Install Platinum then install BandLab Assistant and CbB.

You can download Rapture and Dimension Pro plus any and all Expansion Packs for them by Clicking on your Name in the top right portion of this very page or logging your Cakewalk Account  from your browser.
 Once logged into your account Click on the "My Products" tab, and everything you've ever purchased from Cakewalk is available for download, including S/N numbers needed to "Manually" activate older software like Rapture and Dimension Pro that was released well before CCC.
 I recommend burning them to CDR
 
 If you were lucky and wise enough to purchase Rapture Pro, that can be reinstalled and registered automatically from CCC.
 However, you will still need to download them and additional add on Expansion Packs you had previously used Rapture and Dimension Pro for them to be listed and accessible from Rapture Session and Pro's patch browser.