Well thats just it I dont think there is a need to modify the figures as Legionaries are still recognisable as such at least untill after the Marcomannic wars, all the changes were gradual over decades, though as I said there are some detail differences so a new set wouldn't go amis....
The problem there is a disparity between the art and archaeological evidence, obviously actual artifacts cannot be in doubt but are rarely complete even if the components are common, the accuracy of art is always open to question...
Many details would be likely to small to notice in 1/72.
Armour would be scale, mail and plate, arm defences and greaves, helmets would have deeper neck guards but otherwise recognisably Imperial Roman.
Scale armour exists in several types with new versions, semi ridged scale with a pair of plates at the neck and scale/plate also with the neck plates, scale shoulders and plate lower body similar to segmentata.
Mail, There are apparantly no mail closure hooks though I would note there appears to be an example from the much later site of Dura Europos but this may be an anomally..
Plate armour would be lorica segmentata in a simpler form, although other forms may still be about.
So essentially the figures have a mixture of armour that is consistant with the time though may differ in some minor detail.
Swords and scabbards (on the right for legionaires at this time), Sarmartian type pommel ring swords seem to be popular and replacing the older gladius, scabbards are mounted with a slide and baldric, the pugio is still in use.
Shoes, low closed shoes/boots are now universal.
Clothing, no real change though long sleeves on tunics are fasionable with the civilian population, trousers not yet. The Paenula a sort of poncho goes out of fashion to be relaced by a cloak the Sagum.
Cavalry, Sarmatian type two handed lances seem to be in use so no shields.
For reference see:
"Roman Military Equipment" Bishop and Coulston.