Changing the “m” or “b” would change the overall line on the graph. Meaning the line could be steeper or flatter. It could also change whether the line has a positive slope or negative. Likewise, when you use negative numbers for the m, the line will have a negative slope and will have a decreasing look to it. When you use negative numbers for the b, the y-intercept will be negative which will put the line further down the y-axis.
I hope this is what you were looking for! I kinda did it off the top of my head so of course feel free to change anything!!