I think Elongated Man could do with a name change he could go by the name either 'Freeform' or 'Flowform' because he manipulates his own body.
Brion's codename 'Geo-Force' sounds like a cool name for The Melt. I din't mind 'Geo-Force' as a codename but I think it would sound better as an elemental force, Brion could go by the codename, Tremor, Igneous, Paradigm or Worldtamer.
For Gypsy maybe she could go by the name, Pathway or Crossroads?
How about Traveller?
Tremor or Paradigm are my choices for Brion. "Freeform" would work more for Plastic man. Unless you wanna play up the irony as I always saw Ralph as a bit uptight.
I know "Batgirl" is snappy to describe a single character but if they're going the Batgirls route we can totally have like, "Spoiler Batgirl", "Oracle Batgirl" and "Orphan Batgirl", their alternate codenames becoming descriptions of which and what kind of Batgirl they are in the agency. I'm not sure how else to roll with it without it getting too cutesy. Spoilbat and Blackbat? Yadda.
I'm not sure I'd go for that, but we all have our own headcanon.
Any black character with black in their code name needs a change (BL's an exception since it's long been justified by giving him literal black lightning):
I...disagree. If it can be justified in Black Lightning's case it can be justified in anyone's case. Also I hardly think Black Racer needs a name change, it fits well enough.