sinsofgmat wrote: My question is on the opening modifier.

Dressed as a man and using the name Robert Shurtleff

How come a verb-ed modifier parallel to verb-ing modifier.

Dressed as a man and using the name Robert Shurtleff, Deborah Sampson joined the Continental Army in 1782.
Here, dressed and using both serve as ADJECTIVES modifying Deborah Sampson, the subject of the following clause.
Thus, the two modifiers are parallel.

One modifier is VERBed, while there other is VERBing, in order to convey the intended meaning.
An introductory VERBed modifier implies an action completed BEFORE the main verb.
An introductory VERBing modifier implies an action taking place AT THE SAME TIME as the main verb.
Here:
dressed correctly implies that Deborah Sampson put on the clothes of a man BEFORE she stood in line to join the army.
using correctly implies that Deborah Sampson was using the same Robert Shurtleff WHEN she stood in line to join the army.
If the first modifier were dressing, the implication would be that Deborah Sampson was putting on the clothes of a man WHILE she stood in line to join the army -- not the intended meaning.