I use a 25 W soldering iron, too - never had any problem by paying usual attention.
Regarding connectors, personally I would follow the "two mics, one plug" way, because of its reliability. The previous version of my EM 172 was terminated this way - putting some heat shrinking tube over connector and the final part of the cables completed the work and made everything nice and resistant.
Personally I didn't find anything about rewiring or modding....