Is it permissible for men to use women's sanitary pads in times of necessity or at night to prevent seminal discharge from soiling clothes, if the intention behind their use is good?

Semen is pure, and what you are doing is a type of waswasa (whispers of Satan/obsessive doubts). The cure for waswasa is to abandon it and turn away from it. It is preferable and more cautious, when taking precautions against semen, to use a pad that is not specific to women, out of fear of blameworthy imitation. For the Messenger of Allah, peace and blessings be upon him, cursed the man who wears women's clothes and the woman who wears men's clothes. Blameworthy imitation is that which is exclusive to the other gender or predominantly associated with them in their gender, appearance, clothing, speech, and all their affairs.