Even with a TLJ helmet some of the armor does need work to be approved, joining and filler some areas is needed, either ABS paste sand and polish or filler and paint.
Differences between the two are
Helmet, lots of differences, clips, shape, teeth, frown, and of course the shape/details of the clips as well as extra gap around the clip in TLJ/TROS version
TFA Anovos (albeit there was the premier fiberglass and at least 2 plastic versions so they may vary)
TLJ screen used helmet, note the gap around the clip and shape/details compared to TFA
Denuo Novo TLJ has similar clips and no gaps like the TFA Anovos so it's not very screen accurate.
Justin @TheRascalKing offers 3D files for helmet clips, you would have to change sizing to suit your helmet
Cod
Forearms
Anovos/Denuo Novo have a step, similar to Finn but still not quite right, many add a filler piece of ABS and add ABS paste, sand and polish, Justin has a nice DN build here
Detonator
TFA
TLJ has a separate pipe as well as cut out on the housing
The TFA TDS were solid resin and weighed 1.5kgs. For TLJ they completely redesigned the TD, cut-out the apertures and created a lightweight insert.
There are also some difference in the blasters, more info in this thread
At the end of the day it's all down to your GML (garrison membership liaison) and what he/she/they will approve at base level, some are stricter than others, some may miss small details, detachment only looks after the higher level approvals L2 and L3, more detail info on higher levels you can contact the @Deployment Officer Team and also check out the CRL's (costume reference library)
TK - Stormtrooper: The Force Awakens
TK - Stormtrooper: The Last Jedi
First Order Battle Group for everything FOTK related
Locating your local 501st garrison https://www.501st.com/maps/