So will 5G have a upgrade in few years time to 5G MAX or 5G+ or 5G ultimate or whatever they wanna call it?
Yes I think it will happen since like 3G and 4G there's a lot upgrades on this type of networks, maybe when 5G officially announce that all of countries must have this network it could probably upgrades after years later.
Do these mid life upgrades require new hardware masts/satellites/towers?
Well, if the 5G network is different from 3G and 4G It should require new set ups including hardware, towers or even satellites.