I have SM G900A android 5.0 G900AUCU4BOF2

Is it possible to root and wipe cert/write new cert? I keep reading it's not possible but I need some firm answers. Any guidance appreciated, Thanks!

Sorry the title should say SM G900A not N900A

downgrade to 4.x, enable diag mode with *#0808#, wipe/repair security, write the cert.

Hello.

To perform "Write Cert" operation You need to do the next:
1. Root your phone manually.
2. Perform "Wipe Security" operation
3. Perform "Write Cert" operation.

Cert files are available in "samsung/for unlock and repair/cert" folder of the Support Area.
Note: at first, You might need to enable CP logging from Recovery Mode, so that phone could be detected correctly by PC.