User has an existing dimension on the drawing associated to some sketch curves but is unable to edit it to make it manual text.
To accomplish the goal, delete the existing dimension and create a new one. Before placing the dimension on the drawing, set Driving Method from "Inferred" to "Driving". Since the new dimension is no longer being driven by the sketch curve, you can edit the value and change it to manual text using Menu-> Edit-> Annotation-> Text.
Notes and References
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