1 - No, currently we do not support running the appserver as a user other than bladmin. No plans to change this in the near term as far as I'm aware.
2 - This should be fine if the bladmin user and group exist before executing the installer it will not attempt to create the local user. I think we have some info about this in the docs and/or KB. I'll take a look.
Thx for the feedback.We now run with a local bladmin but might have to change to an LDAP based one due to regulatory reasons.