There are too many instances in which your established symbology is overruled by a minor revision. This has been documented elswhere as it occurs inside the label manager. Here, I would like to address the layer properties' Symbology tab. If you have multiple lines symbolizing various categories of your feature and then decide you want each of them to have an additional underlying white line, or all to be a bit larger, or all... anything, then you can right-click, and choose "Properties for all symbols." However, any action you take from that point (other than changing line weight) will result in you losing your previously determined colors. So in order to perform such revisions, you'll have to go through each and every one of them individually.
