Can you add a link to the SE post?
I agree more details about the final goal would be on point as this looks like a XY problem. Meanwhile, here's what I can add:
boxes = RowBox[{"c", ToBoxes[Plot[Sin[x], {x, -2, 2}]], "a"}];
boxes is a typeset/box representation of a product: c Graphics[...] a. Where did it came from and what is your plan? If you only want to display it:
RawBoxes @ boxes
If you want to convert it to an expression but keep the input order:
ToExpression[boxes, StandardForm, Hold] (*HoldForm or whatever you need*)
But if your initial plan was to put c next to the plot which is next to a then why not:
Row[{"c", Plot[Sin[x], {x, -2, 2}], "a"}]
