Absolutely, they fight tooth and nail to keep load testing to an absolute minimum - it's a very expensive and time consuming occupation.
In this day and age, static testing is not an absolute, it's part of a wider strength analysis, and is mostly used to validate a complex combination of finite element analysis and supporting manual calculations. It will also almost certainly have been done based upon company predictions of the long term weight increase that derivatives of that aircraft will need.
Where part of that structure is modified later in life, proof of that is mostly by analysis, based upon the records that exist of previous analysis and testing. There are two ways in which this can be done - one (the complicated and expensive way) is to re-stress and, if necessary, re-test everything. The other (the cheaper and easier way) is to prove that the modified bit of structure is "no worse than before" from all relevant strength, inertial, flexural and resonant viewpoints. This goes on all the time, not so much from a lightening viewpoint, but usually as in-service problems, areas prone to fatigue, the need to add a new box of electronics somewhere goes on constantly through the life of the aeroplane.
G