Bolt mod is important because as more of those round plastic rivets break that hold together the internal parts, it will affect the quality of the key presses. You may have missed key presses or ghosting from the loosened internals.
If you are going to bolt mod, I always recommend taking apart the whole thing so you can clean any internal parts. I've done a couple dozen bolt mods, and I've never kept the parts clamped together. There are so many guides on the process, that it is not that hard to figure out, you just need to have the proper parts and tools.
To document the rows and columns you will have to take apart the internals and examine the membranes. You'll notice there are dots that are connected by lines. Obviously, the dots are where a key presses down and those connected lines make the rows and columns of membrane matrix. The membranes also have two ribbons that slot into the controller. All of the lines for your columns and rows are going to terminate at those ribbons and neatly align at the ribbons.
To create a copy of the membrane that I could write on, I just put a piece of paper over the membrane and lightly traced all the lines and dots.
Now take a look at this link here:
http://phosphorglow.net/2015/06/24/matrix-maps-charts/Notice there are two letters for each dot or key on the keyboard. That is the identifier we are going to assign for each key in the firmware when we get there.
Rows are going to be the first number for each dot, with the furthest left row as 7 and then count your way down to zero.
Columns are the second number for each dot. Start with zero on the far left column, go all the the way to nine, and then turn to letters. My wheelwriter had 0-9, and then A-C.
Trace the lines to see how each dot is connected to the rows/columns on the ribbon, and then write down the row/column next to each dot/key
That's as far as I have gotten because I have not tried to mess with the firmware. But what I'm going to do is take the SSK firmware from the page I linked above, and adjust that more my matrix.
Now I know that my explanation might be confusing or may not be the best way of doing things. Ask any questions if you have them.