Ask for a change (“add a peripheral compartment with WT on Q”, “make the error model combined”), paste a NONMEM error, or ask about the code. A router picks specialists (structure, variability, covariates, estimation, syntax, run doctor); every draft passes the NM-TRAN checks and a simulation, and a reviewer checks it. Its edits appear in the editor as it works, and one Ctrl+Z undoes the whole change.