The reason why they do not do more than 225W is because the case design sucks and they have major heating issues which blow out their capacitors. DO NOT mod the case to use any performance parts as you will bake them and break them. In fact they are such a problem that we no longer use them at my work (Cincinnati Computer Cooperative) because they ALWAYS come back with problems. If you require more than the 225W then get a proper case with good airflow and start over in that, or at least upgrade the motherboard with something that has solid state caps inside which can take the added heat you are putting in.
As for the mod, no, it is not particularly dangerous to do (as the PSU housing will protect the user from frying themselves), it is just a generally bad idea because it was designed for a particular configuration and you will run into other issues down the line by modifying it.