The Cooper loading in the AREMA manual is intended to be scaled up and down according to the loading specified for the design. If you look at the history - in the early years, railroads designed to Cooper Loadings as low as E-40 (and the AREA manual of the day showed the E-40 set of wheels, exactly half of what is currently shown as E-80). A Cooper E-90 design loading is currently specified by several railroads for permanent structures (that may be expected to be in service for 100+ years. It will be several decades before the loadings that railroads are actually running reach this level.
Your charts (presuming they only show the live load effect so we don't have to account for not scaling the dead load pressures) can simply be scaled upwards by 12.5% to get the equivalent E-90.
I don't know the specifics of your situation, but even on a heavy haul mainline track, it seems to be overkill to design a TEMPORARY shoring system to such a high standard since current North American rail traffic (heaviest 286 kip cars = 71.5k axels) rates in the vicinity of E-60-75, depending on what they are running on.
Also, don't forget to use the alternative cooper loading cosnsist of four axels(100 k axels for E-80 = 112.5k axels for E-90)