Ed T,
See what happens when one retires from an industry after 41 years as I did in 2007, new stuff keeps comes along.
Certainly, there are & have been conversions for the 3 electric wheel truck where it is relatively easy to switch from a pneumatic style to cushion tire & vice versa but not inexpensive - but three wheelers units were initially designed to "go both way".
And while working with a Japanese F/L company we "toyed" with the idea of installing cushion press-ons on to a pneumatic electric chassis, even had prototype unit. This is feasible as you are dealing with a longer wheel base & wider frame & installing a tire that will deflect less ( lift capacity rating is not compromised).
But the initial question asked in this thread was about converting/modifying a "cushion tire unit" to incorporate "pneumatic" tires. The major issues are smaller frame (width & wheel base length) & installing a tire that has more deflection (i.e. pneumatic) - plus a host of working clearance issues both at the drive tire & steering tire end. Pneumatic tires of comparable load capacity rating tend to be significantly larger in diameter & wider than a press-on cushion.