You can freeze, turn off, change color or linetype, etc in your file without affecting the attached file. By default, in curernt releases, the variable VISRETAIN is set to 1 (on), so those settings will be retained in your file.
You will have to watch for bad drafting on the part of the people sending you drawings. One lazy, or overworked drafter at their end who cuts corners - sets a color explicitly rather than bylayer, or who puts data on the wrong layer will screw you up, and you will have to fix it. ( I used to work with a woman who drew everyting on layer 0, and then match propped it to somethign existing that was the right color, but it was frequently on the worng layer, it just had the right color)
Message was edited by: c.prettyman