Frog,
I had a similar issue with a Chambers' patchbox latch spring and did two things to reduce the pressure required on the release button. First I filed a slight draft on the end of the button rod such that it contacted the latch hook bar as high as possible. While this changed the contact point only very slightly, it did make a small difference.
Second, I filed the latch spring. I read here that filing such a spring on the "flats" has eight times the impact on lessening the spring strength as opposed to filing on the side. So I filed the sides a bit and tested, again and again. It didn't take too much filing to adjust the spring strength to exactly what I wanted.
Hope this helps.
Bill