S/4HANA adding resources to engagement project using Custom Logic

Hi,

We are using S/4HANA Public Cloud for Professional Services and would like to add a number of team members automatically to a specific work package when the user changes the engagement project stage to "In Execution".

We will have a Custom Business Object containing a list of users that are to be added, depending on a Custom Field (Service Line) in the project.

We would like to implement this using Custom Logic but unsure which Extension Point should be used for this. The obvious one is /CPD/ENGMT_PROJ_SAVE.

However it seems the logic that can be implemented is very limited

Can anyone recommend an Extension we could use for this, or suggest an alternative approach.

Thanks

Thomas