It's quite possible. For the past 4 months I've been conducting controlled experiments with a 67-1, a 620, a 610-4, and a 617 no dash. BTW, those experiments led to some conclusion that are a bit counter to what is commonly believed. One of these misconceptions is that the spring for the rebound slide has a significant effect on the DA trigger pull, I've determined the effect on the DA side is so minor it can be mostly ignored. However, the spring for the rebound slide has a significant effect on the SA trigger pull. As for the mainspring, it's effect is ALL on the DA trigger pull, the effect on the SA trigger weight is so slight that it can't be reliably measured. Following is a summary of what I've learned.

The spring for the rebound slide has most influence on the trigger pull in Single Action. With a fairly recent gun that hasn't had the sear on the trigger stoned for a lighter let-off, using a 14 lbs. rebound spring will yield a Single Action pull in the range of 3 lbs. give or take 2or 3 ounces. Use the factory 16 lbs. rebound spring and the SA pull will be right about 4 lbs.

For the double action trigger pull, again on a recent unmodified gun, reducing the length of the strain screw by 0.010 inch will yield a 9 lbs. DA trigger pull with that previously mentioned 14 lbs. rebound spring. With the 16 lbs. rebound spring the DA pull will be about 9.5 lbs.

If you want to go any lighter with the DA trigger pull it can be done, however I have only done this on models with frame mounted firing pins and I've found that the use of an extended travel firing pin is required to maintain consistent primer ignition. With my model 620 set to an 8 lbs. DA trigger I found that while there were no misfires, the accuracy degraded from what I was getting with the trigger at 9 lbs. Installing an extended travel firing pin from Cylinder & Slide brought the accuracy back to what I was getting before lightening the trigger from 9 to 8 lbs. As for why the accuracy fell off, I did a bit of reading on the internet and several articles indicated that it's possible to get a primer to partially ignite, when that happens the result is a variation in velocity from shot to shot and the result will be vertical stringing in the groups. Quite simply, when you start getting near the point of misfire, accuracy will degrade unless you take some steps to insure complete ignition of the primer. With the frame mounted firing pin this is pretty simple, add a firing pin that allows it to travel deeper and if needed, Apex Tactical also offers a weaker rebound spring for the firing pin.

As for how I got the 620 to 8 lbs. it was pretty simple. Installed a 14 lbs. rebound spring and reduced the length of the strain screw by 0.020 inch. I've also been using Speer Lawman to test for reliable ignition because of Speer's reputation for hard primers.

Note, at 60 dollars I think that the Lyman digital trigger gage is an excellent investment if you plan on doing your own trigger tuning. I tried using a cheap spring type scale and it was difficult to get a good repeatable reading. The Lyman is very easy to use and the pull to pull variation is normally under 3 ounces. I'll also note that I consider a rebound slide tool an absolute MUST, I cannot imagine attempting to install a new spring in the rebound slide without one of these tools. You'll also want the Kuhnhausen S&W Shop Manual, it's essential in proceeding in the correct sequence and has invaluable tips.

I'll also note that it's a good idea to have at least one and preferably two spare strain screws on hand when you start. I've been using hand made shims made from shim stock that fit under the head of the strain screw in my experiments and they are a bit tedious to make (Dremel and diamond burr, 0.147 ID and 0.215 OD).

Note conderning hammer mouunted firing pins, and at this point it's a conservative recomendation. With the hammer mounted firing pins I would stop with the DA trigger pull set to 9 lbs. Unfortunately with this type of firing pin you don't have the option of using an extended travel firing pin or a lighter firing pin rebound spring. At this point I have an older model 67-1 set to a 9 lbs. trigger and it works perfectly so I'll just leave it as it is. BTW, with that same 14 lbs. rebound spring the SA trigger breaks right at 3 lbs.

I also have a 610-3 setup to the same weights as the 67 using that same 14 lbs. rebound spring. Finally, a 617 no dash that I picked up used is set to a 9 lbs. 3 ounce DA pull and with a 14 lbs. rebound spring the SA pull is 2 lbs. 4 ounces, a result of the previous owner stoning the SA sear on the trigger. Pretty soon I'll go back into the 617 and sharpen the SA sear on the trigger to the factory angle because currently it's lighter that I like and in time that "assist" angle on the trigger sear could lead to a pushoff problem. As difficult as it is to get replacement hammers it's best to leave the SA sear on the trigger alone and adjust the SA trigger weight by using an appropriate rebound spring.

Finally, don't take my recomendations for the strain screw adjustments as being cast in stone. While in my case the progression was consistent from gun to gun I expect that there is some variation in the "set" of the mainspring, meaning that you want to tune specifically to weight and use the dimensions given simply as a guide. In addition on an older gun with some past history, it's quite possible that the strain screw may have been shortened previously or has worn shorter with use. On my 67-1 the strain screw matched the length of than in my 620 but when I went into the action I found the rebound spring had been trimmed shorter.