Use Layer Property Filters to filter all the layers in your drawing to a manageable few.
Say you need to quickly set all the existing layers to a screened line plot style; a filter will allow you to display only those layers, and then you can make global changes. The Properties Filter button is found in the upper left corner of the Layer dialog.
Name the filter Existing, and enter the property criteria that will match only the existing layers, in this case we enter *-EXST under the Name property. (The star is a wildcard to match everything.)
Now use the Existing filter to limit the layer list to only those that end in -EXST. Select All and set the Color to 8 (gray) and/or the Plot Style to 40 (40% black) to get a screened line effect. You could also use this same filter to select the demolition layers for freeze/thaw or on/off.
You can use the same process to create a filter for -DEMO layers. You can even reverse this by creating a filter for new/proposed. Here's how: create a filter named not New and enter two lines for the name criteria, *-EXST and *-DEMO. The new filter will display only existing and demolition layers. Use the Invert filter in the lower left of the Layer dialog to show only layers that are not existing or demolition, making it in effect a not not New, or New, filter.
In these examples, the filter criteria has been the "Name" property, but you can also filter on other layer properties: color, linetype, lineweight, etc., or a combination.