An SLA-type Service Target will not honour changing of the Business Entity field configured in the 'SLA Type Reference Field' on the data source unless you are switching to a new SVT, reopening, causing a restart etc. ... something to cause the creation of a new SLM:Measurement record.
An OLA-type Service Target will check for a new value in the 'OLA Type Reference Field' configured in the data source. When you configure a field in the 'OLA Type Reference Field' and rebuild the data source, an additional filter is added to the data source filter guide specifically to check if this field has been updated.... but for OLA Service Targets only. This would be more suited to your scenario where the Business Entity needs to change during the life of a single SLM:Measurement.
I'm not sure that it would necessarily honour the new goal time but it would certainly switch Business Entities and recalculate the Due Date/Milestone fire times etc. based on the new Business Entity.
Hope this helps!
This is good information and I have read it in other threads. I tried the OLA method and while it does notice the change in the Business Entity, it does not notice the change in the number of seconds for determining the end date/time. I'm thinking I may need to submit this as an enhancement request as the tool (IMO) SHOULD do this when the end goal changes.