That recommendation you want to give is safe enough for you and should work for the system, if you were going to tweek it though, you can generally get to the internal expansion valve adjustment through the flare nut on the outlet end, turn it in 1 full turn, that will starve the coil so that it will work better with a 4 ton condensing unit.
There will be no liability in that mechanically, same with slowing the air down 20%,
If that 270 psig head pressure is accurate, either its a two stage compressor operating on low stage, OR something else is incorrect, Head pressure at 80F outside requires a *coil temperature 25F hotter so thats 105F and 341 psig head, (the air off the coil however will only be 15F hotter)
Someone may have put some R22 into that system... watch out.
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