Well if the regulatory agencies decided that they weren’t going to act then I suspect there would be a grass roots level spread of the strain anyway. This would be the worst way to use such a strain, but I don’t think it would be possible to stop this happening.
I don’t think we will get to that point. If we collect good data from the natural spread of any attenuated strain then I think the regulatory authorities will allow its use on the basis of this data.
Send people infected with the harmless version around, after lockdown ends in a month or two, to crowded places?
Would greater virulence be a desirable quality in our reduced strain?