This will definitely work, the current however may be off (probably not much even if you'd use 9uF alone). Most of the capacitors used in ligthing are self healing types and are used at fairly close to their rated voltage, which means that they do degrade in their capacity over time. I would imagine that even luminaires where the capacitor is long gone from it's original value still work

 Thank you Ash! While Philips did offer them in 300V ratings I have only those motor run caps rated 450 and 475V respectively.

In Fluorescents for example, the capacitor used in SR105 ballasts is nominally 6.8uF, in fact both 6 and 7 uF appear to work fine, and it fails (slow or intermittent starting) when it degrades to the 4..5uF area, to scale. I'd imagine that in a SOX application a degraded (or just undersized) capacitor will be able to run the lamp but not fully warm up

Yes I had in the past some experience with such depleted series capacitors in fluorescent lamps. The lamps just refused to ignite.

Use capacitors that can handle the working current continuously such as motor run capacitors

Yep I have only such capacitors. However their quality is not that good (Ducati from Italy)

Definitely don't go up in capacitance, as that might increase the current, and depending on the ballast design it might be even quite significant for relatively small capacitance change

I think that this ballast is of CWA type, looking at the wiring diagram in the catalogue.