If the 505 electrode was not used in the weld procedure qualification for the plate that was welded, it needs to either be removed or the procedure requalified with the E7018 and 505 combination in the same joint to meet most codes I am familiar with. You'll also have to discuss this with the customer or design engineer if you plan to requalify the procedure and leave the 505 in the weld. It may be quicker and less expensive to get out the arc gouge and/or grinder, remove that section of weld, and reweld with the correct electrode. Being over budget is no justification for not doing the right thing.
Marty