When the EEC-IV senses an emissions system failure, most times it will just disable it and set a code. However if it's a failure bad enough it goes into FMEM, or limp mode. I have yet to see an FMEM condition due to EGR, though. EGR isn't important at WOT because it's simply shut off completely. On the other hand, the computer takes a holistic view of the engine regarding how it responds to different conditions; by this I mean on the street and normal cruising conditions -- where it spends the majority of the time learning more about your engine. This means that if you don't have EGR, it will not only sense the EGR valve not opening, but also a richer condition than what is supposed to be. Installing a resistor isn't going to work since the computer executes a command to control EGR flow, then looks for a corresponding signal to verify its operation.
If you plan on having this car as a daily driver, I'd leave the EGR and air pump on there, if nothing else just to prevent codes and any compromise in driveability and mileage.
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch