If a Muslim performs ablution (wudu') and wipes over his khuffs (leather socks), then takes off his khuffs during the period of wiping before prayer, does his ablution become invalid by that or not?

Purity (taharah) is not invalidated if one removes the khuff (leather socks) or jawrab (socks) after wiping over them, because the purity was completed in accordance with the Shari'ah evidence, and there is no Shari'ah evidence that nullifies it by removing what was wiped over. Therefore, the ablution (wudu') remains valid. However, if one wishes to wipe over the khuff again after the ablution is broken and they were removed, then they must be worn while in a state of purity where the feet were washed.