This is a 'duplicate check' 😕
It's straightforward for objects that are instances of the same component with the same insertion point / transformation, in the same context... copy/paste+<enter> this one-liner in the Ruby Console - it works on a selection containing component-instances...

m=Sketchup.active_model;s=m.selection;a=s.grep(Sketchup;;ComponentInstance);s.clear;d=[];a.each{|i|next unless i.definition.instances[1];t=i.transformation.to_a;(i.definition.instances-[i]).each{|e|(d<<i;s.add(e))if !d.include?(e) && e.transformation.to_a==t && e.parent.entities==m.active_entities;};};

The duplicates are highlighted on completion. If you start with Entity Info open it will show what's selected still etc... Pressing <delete> when the SketchUp window has focus will remove the duplicated item...

It gets more tricky when they are 'symmetrical' and perhaps placed overlaid 'handed' - therefore with different insertion points but seemingly occupying the same volume.
A matching bounding-box check could work BUT is not foolproof... I think thomthom might have done something like this ? Do a search...

You would likely find it useful to set the text for text boxes and labels while you're at it. As TIG says, if you find you always need to change text size to something else for new projects, you should be making a template that is appropriate for your use.

You can also sample an existing text box or other entity and apply its characteristics to new ones going forward by selecting the tool, Dimensions in your case, and hitting S. Click on the already modified dimension to sample it and go on with your dimensioning.

CamnCam,
See this DC that I created a while ago, it may give you some help:
http://sketchucation.com/forums/viewtopic.php?f=289&t=21350
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I suspect that the real problem you may be having is with the framed object corners ???
ie You want to change the overall size of the frame eg make it taller or wider but at the same time keep the frame members a regular size eg 50 x 50 ???
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One trick is to use some hidden cubes / rectangles in the corners + some lines on a layer that you hide eg Give a Layer the name "Hide" etc or hide some geometry.
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See DC above
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Hope this helps.
Howard L'