"Can I install Media Agent of DP 9.0 alongside the Media Agent 6.2 on server A?
Nope, you can only have one version of any components installed on any client machine
==============
"But can I uninstall 6.2 Media Agent on A and install 9.0 Media Agent there leaving DP 6.2 Cell manager installed just in case I will need to look at some configuration data there?"
You can't uninstall any component, you would have to remove all of DP from that server, and reinstall.
You might ba able to delete, move or rename any executables with 'ma' in the filename, for example
bma
rma
mma
uma
then install DP 9. This is totally unsupported, and you would be on your own. On a windows Media Aent, there may be some registry issues involved
==============
"just in case I will need to look at some configuration data there"
What kind of Configuration Data are you wanting to Review? Most anything of any use can be captured with these commands, redirected to a file
omnidownload -list_libraries -detail
omnidownload -list_devices -detail
You could do this before moving to DP 9