If you exceed the 2.63 you should remain there for 90 days. *1
Adding weight after you have exceeded 2.63 doesn’t work as the w/kg uses the weight at the time you exceeded the 2.63. (It is a bit more complicated than just one weight being used)
*1 - it has been known for zFTP to reduce within 90 days as other power numbers for various other time intervals affect the zFTP calculation curve.
EDIT : hopefully Zwift’s new Racing Score categorisation system based on results not power will arrive early in 2024 and put an end to power based categories.