it doesn't seem to me that it would be that difficult to surgically/biologically modify a human to survive durations of up to an hour or two in a vacuum, a windpipe artificial sphincter that closes the throat when oxygen partial pressures in the lungs are lower than in the blood to stop oxygen loss ( still low enough so your lungs dont rupture), massive vasoconstriction to increase mean arterial blood pressure so gasses dont dissolve out of the blood and cause heart fibrillation and stop circulation, and some gene therapy to modify myoglobin concentrations and charge like a seal, incorporating the 16 amino acid sequence behind crocodile haemoglobin allosteric effects in human blood ( makes the release mechanism for oxygen more efficient) and the up-regulation of glut5 pumps on oxygen heavy organs so that when oxygen levels decrease fructose anaerobic metabolism can cover the difference like in naked mole rats. non of these modifications are actually that large scale and the benefit of not dying/ going unconscious after 15 seconds of depressurisation for space colonisation is immense