Dewalt DCS391 - Can't change blade on circular saw because of stuck blade clamping screw
Following up on how I've resolved this and what was the issue. At the time of this post I've tried everything that was suggested and the clamping screw did not bulge at all. However, I did not had access to was pneumatic tools in my shop at home, so I went to a local tool store and they dislodged the clamping screw for me. 

They explained to me my mistake and why I had such a hard time removing it. The issue was that I've inverted the washers (r, s) and they were not in the correct position.

Here's a picture of the circular saw once it was correctly assembled with the r and s washers in the correct position.