it really depends on the ballast if it is a parallel ballast for 4 bulbs and or a split for paired 2 w\sets of 2 if it is a parallel no you cant if it is a split 2 pairs of 2 you can

you will have to get an internal schem of the ballast you might be able to decipher by looking at the external

but the reason for my answer is it will cause an imbalance if it is a parallel 4 and the long tubes may not light and if they do they wont get the energy they require and be dim electricity takes the path of least resistance meaning the shorter tubes will be that

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