You have been feeding him too small of a prey item for years. Mine is a year old and he is on medium rats every 8 days. The reason he has become more aggressive after feeding is because he has more food in his stomach and it would be harder to defend himself because he can't move as fast. Just dont bother him after he eats for a day or 2.
Think about it... This snake is a wild animal its not going to hurt them if they swallow a little substrate. Intestinal blockage is very rare I have been feeding on aspen for years and never had a problem. And the myth about feeding them in a separate cage does more harm to the animal than good. Feed him in its cage and don't pick him up after eating.