In the scenario you described, where photons A and B are momentum-entangled and you measure the locality of photon B just before photon A passes through a double slit, the result of your measurement on photon B should not have any direct influence on the interference pattern observed from photon A.
Momentum entanglement typically refers to a type of quantum entanglement where the total momentum of the entangled particles is known while the individual momenta are uncertain. This means that the entangled photons have correlated momenta, but the exact values of their momenta are not determined until measured. Consequently, measuring the locality of photon B should not affect the behavior of photon A as it passes through the double slit.
The interference pattern observed from photon A passing through the double slit is determined by the wave nature of the photon itself and the experimental setup, such as the distance between the slits and the screen, the wavelength of the photon, and so on. This interference pattern is a result of the superposition and subsequent interference of different paths that the photon can take.
Therefore, regardless of your measurement of photon B, the interference pattern observed from photon A passing through the double slit should remain the same, assuming all other experimental parameters remain unchanged.