modify extension line by dragging extension line end handle dynamically

The dimension could be associated to an element which would prevent manual resizing of the dimension. Either resize the element or drop the association and then resize the dimension,

Which way are you trying to drag the extension? Are you trying to drag it in manner that will change the value of the dimension (make it shorter or longer) or are you trying to drag it to move it so the dimension value is closer to or further away from the element being dimensioned? Could it be that you are trying to make one extension line longer than the other?

A few screenshot would be helpful but, what @Barry Lothian has pointed out is the first thin I would check on.

In v8i there is the modify dimensions tool to make this easier, ( I expect its still in CE too)  but it also depends how you want to modify your dimension the normal modify tool works for me  but as  wlong says just  how are they trying to do it and what result is expected.

here are two pixs , by  first  principal no fancy tools, I click on the dimension via selection tool or power selector ( dims now in magenta highlighted) and I / we can now  see the handles so if  I want  to move the outside left dim to get the green element so I select the drag handle near the bottom of the dim extension line  but on the  blue object its associated to and drag it to snap to the green and object left side of the screen  in the second pix you see the result.

and result is dim changed from 3.5 to 4 real dim values, notice still a section set ( highlighted magenta and handles visible)..

if I want  to  move the dims up or down  closer to the element then select the  dimension line below the text in the dim and drag in the direction  ie up or down magenta is the selected dims, and the dragged yellow and white result is  previewed in the new location if I accept. then the change  happens, below is preview dynamic before data point to accept the changed positions..

Eazy peazy....

I suspect your engineer has the handles disabled in the power selector  or needs a little  microstation training.. as I would if I went to use revit...