Section 5.4.3 of the standard refers to NFPA 13 \"Standard for the Installation of Sprinkler Systems\" when maintenance or repair involves more than 20 sprinklers. This section is intended to address common installation issues such as pipe, fittings, hangers and so on.
It is sometimes a common practice to hydrotest a system without sprinklers installed, i.e.: with ½\" plugs installed in the bottom of a drop to a pendent sprinkler and then install the sprinkler after final adjustment of the drop once the finished ceiling is installed. Both standards are silent on this issue. My suggestion is to consult the local fire marshal to determine what he/she will accept. In most cases when replacing sprinklers only, and not modifying the pipe, a hydrostatic test is not required.