That is what exactly I think the Wuhan labs was studying, given that SARS did jump from another animal to human very recently. What would happen if these things mutate naturally and infect humans? They add gain-of-function genes to a near relative, study how it infect cells and come up with a plan to treat it. Except someone dropped some stuff on their shoe and went out shopping to the wet market.
I did plenty of these gain-of-function experiments in my postgrad studies. Mice tumours cells given genes to super-express certain cell adhesion molecules. Without this kind of approach, it is difficult to impossible to study these reactions. You just gotta be careful.