In my .270 Winchester, your top load for a 130 grain bullet and H4831 powder fills the case. If I’m compressing the powder slightly when I seat the bullet, can this load be safe?

There are a number of extremely slow-burning powders that will create this same situation. In the case of these bulky powders, frequently pressure is not the limiting factor in developing a load; case capacity is. You run out of room in the case before you’ve reached maximum pressures, and wind up compressing the charge. In these situations, the compression is perfectly normal and not a cause for concern.