A few years ago we discussed this topic, and it was suggested that bending the little nails which hold the springs one way or the other to tighten or loosen the spring tension was one way to do it. I tried it and it worked for me. It was on my Bb, which was a little tight, so I loosened it up a bit.
Other ideas were also mentioned, such as replacing the springs with longer or shorter springs, or removing coils from an existing spring. But, it was a lot easier to bend the nails, which worked fine, so I never tried other methods.
I should mention something else. On my old Hohner HA-114, the springs were also a little tight in the beginning. But when one or two of them broke, I found out that when you get the official replacement Hohner springs, they are available in different degrees of springiness. So, I replaced the entire set with a less springy variety.
I'm not a real supporter of the nail bending method.
Only because if you are not a skilled bender (Like David ;) you risk damage to the accordion by making the nail hole bigger or possible spliting the wood.
Since you are interested in losening the spring, I think it's better to use a very small screwdriver to expand a coil until the tension is what you want.
You need to be very careful to do this a little at a time, since bending the spring is a "oneway" process. If you "over bend" you will need a new spring, or need to cut out a coil on the old spring.
One way to make it even is to find a weight that will just depress the button when the tension is the way you want it. You can use an old bolt hanging from a string for this. Just keep stacking washers on the bolt until it is the right weight.
Spring set up looks to be the the same as a La. handmade. Fingerboard comes off the same way from the inside reed side. I'm going to give Mike Gabbanelli a call in Houston and see if he can send me a set with lighter tension. Since he offers custom tuning I'm sure this will be an easy fix by just replacing the springs with a different set. Thanks for the input everyone.
On custom built boxes the ounces of pressure necessary to open the valves the buyer requires should be set when he picks up the accordion and subsequent adjustment should be made by the builder with either longer or shorter springs. Nail bending should not be done on quality accordions. It's too inaccurate.