Hi Maddy,
I am closing this thread.
1) Response Profile cannot change dynamically in the service request it is always determined using the SLA determination procedure, if the same needs to be changed dynamically in the service request then you need to go for development
2) Based on the Priority and the Categorization Schema's the first response by and the due by times get calculated- The configuration is done in tcode CRMD_SERV_SLA.
3) For the same service request if the priority or schema changes, the first response by and due by dates do not get changed automatically, however if you do wish to change the same then again you need to go in for development.
Hope this helps.
Kind Regards
Atul