so...i figured something out and wanted to share it with you guys. vRA 7.5 (Hotfix4 VMware Knowledge Base ) has come a long way in regards of custom forms. However there are still some things that are annoying, such as that one must imput Memory in MB. I undertsand that that is a left over from the vCenter API...but seriously...its 2019!
So I finaly came up with a workaround (requires custom forms, vRA 7.5 Hotfix >=4)
1) create a vRO action (I call it memGB2MB) that looks like this:
|Header 1||Header 2||Header 3|
2) Create an custom form of your blueprint and drag at least CPU and Mem on it.
3) Add a new Integer field and call it Memory (GB). Then assign it all the restrictions that the blueprint has in regards of Memory.
(If you havent noticed yet. The blueprint restrictions are transfered ONLY once, when creating a custom form. If you update the Mem or CPU limits in the blueprint later, they are not passed dynamically to the custom form.)
4) Now click on the field Memory (MB) field and go to values. Select external source and then the vRO action you have created and Field Memory GB as the input.
5) You can give the whole thing a go now..or just directy set the Memory (MB) fields Visibility to false.
Well..there is more.
The method would allow you to use a Array/String to display a dropdown menu for CPU and/or Memory. You just need a new action that has as an input a string, as the output a number and the following script: