Is it possible to parallel more than two LT8648S/LT8648SP devices to achieve higher current - example 45A?

Yes, it is. While the datasheet does show a parallel implementation, it only shows a 2 phase design. In theory, it can implement more than 2 parallel ICs to achieve higher current by following a similar connection methodology, however, the point to note here is that the phase angle offset will not be optimal. For example, with 2 phases, you will connect the CLKOUT pin to the SYNC pin of the secondary IC and this will ensure that the phases will be offset by 180 degrees. When you increase this to 3 phases, it does not offset each phase by 120 degrees as the LT8648S does not have inherent capability to support more than 2 phases. There is, however, a way to achieve this. An even phase angle can be achieved by introducing a separate oscillator device called the LTC6902 which can provide up to 4 individual clock outputs - each one can be used to drive the SYNC pin of the LT8648S.

Is it possible to parallel more than two LT8648S/LT8648SP devices to achieve higher current - example 45A?

Yes, it is. While the datasheet does show a parallel implementation, it only shows a 2 phase design. In theory, it can implement more than 2 parallel ICs to achieve higher current by following a similar connection methodology, however, the point to note here is that the phase angle offset will not be optimal. For example, with 2 phases, you will connect the CLKOUT pin to the SYNC pin of the secondary IC and this will ensure that the phases will be offset by 180 degrees. When you increase this to 3 phases, it does not offset each phase by 120 degrees as the LT8648S does not have inherent capability to support more than 2 phases. There is, however, a way to achieve this. An even phase angle can be achieved by introducing a separate oscillator device called the LTC6902 which can provide up to 4 individual clock outputs - each one can be used to drive the SYNC pin of the LT8648S.