if this is a digital block inside an analog module, you can request to the analog designer, the load/drive capability for each pins and define better constraints.
If you want to add this constraint at pad level, you need to know the PCB used, and every think like this, package....
In general, I only apply the set load/drive only for pin between analog/digital, because, this could have an impact on timing. The pad are so "slow", this constraints do not add much info.