the minhag ashkenaz historically was to wear tefillin.
the chassidim and the gra changed the minhag.
those that dont keep any thing chassidish except not to put on tefillin should realize that the chassidim only changed because they lived their lives al pi chasidus and the zohar says not to wear tefllin. someone who does not conduct himself al pi chasidus does not have a license to follow such a minhag.
the proof is from sanz/bobov. all umarried bchurim wear tefiiliin. the reason is that a bochur has no connection with chassidus .
therefor if you do everyting litvish and you run out b4 hallel on pesach nite. you are exactly like a sanz bochur and the minhag insttiuted by chassidus was not meant for you.
of course if you have a legit mesorah from the gra then you are halacha based and not kabbalh based then the above does not apply