Pull assignment values from current assignment for internal candidates in Job Offer

Summary:

We have a lot of secondment use cases in this organization.

This means , when an offer is made to an internal candidate , we need the ability to pull some values from 

their existing Assignment in the Job Offer template.

Is this possible?  I think this link is the answer but am wondering if this would work for getting assignment level values for any internal candidate. Can you query any core hr table this way to possibly pull current salary , allowances etc?

Content (required):

We have a lot of secondment use cases in this organization.

This means , when an offer is made to an internal candidate , we need the ability to pull some values from