Depends if the P90's are ceramic magnet or Alnico V ? Could always convert ceramic to Alnico V or even Alnico 2/3. It's a bar magnet, what are the DCR measurements ? Gibson P90's are +/- 8.0K. Fender MP90's have are about 9.1K per a Reverb item for sale. My 1st inclination is to suggest leaving them alone or finding preowned pickups to replace them with. It the DCR's are in line with what any P90 is from a 3rd party pickup shop, I definitely play them as they are. Ceramic magnets, Alnico Magnets, same DCR's & Henries, all the same to me.
"Fender MP-90 pickups from a Mustang 90. These are standard sized soapbar P-90s that run a little hotter and grungier than regular Fender P-90s. The DC resistance is 9.1k each. The bridge pickup has around 6.25" of wire, the neck has 9". They have some typical pick scratches and do not include mounting screws."