I'm not entirely sure what you're getting at. There are "two levels" of marker in Motion. There are object markers and there are global markers. Globals are set when no layers are selected and they are Green in color. Object markers are attached to layers and are red in color. When multiple layers are selected and moved at once, their markers are moved with the layers, and they are all moved at once retaining the same synchronization as they had before the move. Globals are not affected. They are only moved manually by dragging them individually.
If you are changing other features (in/outs) of the individual layers containing markers, then the timing relationship of the marker to the beginning of the layer will change.
I suspect you are using several object (layer) markers. You *could* create a "null" object (a shape that you turn off the visibility of) and set markers matching your other marker "collection". Move the null object to update/change the relative positions of its markers to be used to readjust the individual markers of the affected layers/objects. (I hope that makes sense... )
You could simply change the length of your project* and offset everything to amount of additional time you added to the project length. If you select the individual Groups, set the playhead at that position and type Shift - [, the enclosed layers will move to that starting **offset** and maintain the timing positions relative to each other. Since each layer's/object's markers will remain in position relative to the beginning of each layer, they will maintain their original relationship to each other, offset by the new beginning time of their parent group. (Does that make sense??)
*Length of project: there are a couple ways to change the project timing once a project has been created —
1) Select Project. Select Properties in the Inspector. Change the Duration (Timecode) parameter (formatted in HH:MM:SS:FF).
2) Click the clock icon under the Canvas. If you have Timecode selected in the dropdown (down caret) menu, then add or retype the time in the clock. If you have Frames selected, add or type in the number of frames the new length should be. You can click and drag the frames/clock to alter time or you can double click the frames/clock and type a value. For the timecode clock, you can use the colon, semi-colon, comma or period key to delineate "segments". There are also shortcuts you can use when typing in time. For example, typing "1.." will set the project to be one minute long (00:01:00:00) regardless of frame rate. However, if you have a 100fps project, you will need to provide a **trailing** zero for "Frames" greater than 9 (e.g. 1..90 for 1:00:90 frames, etc...)
Hope this isn't too confusing!
