Yes. PlanAutomate can be added to an existing Dynamics 365 Finance solution without much disruption.
If you have already implemented the standard Dynamics 365 Finance project accounting module, we will have to close off existing projects and re-create the projects including opening balances within the PlanAutomate data model.
Master data and opening balances aside, a modest level of reimplementation will also be required as many of the processes you have attempted to implement within the standard accounting module will be replaced by superior PlanAutomate capabilities. Because of this requirement, if you have not already implemented Dynamics 365 Finance, it is advisable that you acquire and implement PlanAutomate at the same time as Dynamics.
As a rule of thumb, once PlanAutomate is installed, project accounting and billing is managed by the standard accounting module, while everything else is replaced by PlanAutomate.