Maybe investigate bp_core_render_message(); you could unhook that from template_notices, and re-add your own version to suit your requirements.
@Khairul We’ve just worked on that this week.
Whilst, the template message is stored in $bp->template_message, it is also stored as a cookie.
It’s the text in the cookie that’s predominantly used (on page refresh) for the notice. To overwrite / change the content once a message had been set, we had to change the cookie.
As @djpaul says, if it’s just to strip paragraphs etc. you could look at the filter bp_core_render_message_content.
Unfortunately, the `
` around it is hardcoded in the core function – and difficult to strip out without hacking the core function.
@djpaul — perhaps that’s some output html that needs removing from the core, and moving into the theme in a future release
Tickets and/or patches welcome 
Eek! Okidokies, thank you!