For a single transformer, or a single 3 phase bank of transformers, the polarity is of no importance.
If however a transformer is required to operate in parralell with others, all MUST be of the same polarity.
In theory, "wrong" polarity may be corrected by altering the external connections, but only if each end of each winding is available, in practice most transformers have some internal connections that cant be altered by the installer.
UK 3 phase transformers normally only have 4 terminals on the LV side.
Neutral, and phases A, B, C.
Incorrect phase rotation is easily rectified by swapping any two.
Incorrect polarity can only be rectified by altering which ends of the three windings are connected together as the neutral.
If these connections are internal and sealed, as is the norm, then it cant be altered.
In stand alone use, it matters not, but 3 phase transformers of different polarity can never be paralelled.
"Universal" transformers used to be manufactured that could be connected for either polarity. They were costly items since they required 6 output bushings insulated for line voltage, instead of 3.
The transformer windings were also more costly since thicker insulation was required at each end of each winding in order to withstand switching surges, rather than at one end only.
For his reason British standards stipulate a standard polarity for all power transformers.
Standards in other countries may differ, but the basic principle is the same.