SELinux from disabled to enforcing - is it possible?

[Mike]

Having got one machine running with SELinux enabled very recently I decided to
try to turn SELinux back on for a machine on which I had installed F9 a few
weeks ago and set SELinux to disabled. 

That was a definite no-no - it would not boot once I set SELinux back to
enforcing unless I added "selinux=0" to the kernel line for boot.

I resorted to re-installing F9 and it works fone now with SELinux enabled.

However I now wonder if it was in fact possible to go from SELinux disabled
to enforcing or if this is something which is not possible?

If it is impossible then there perhaps ought to be a health warning asking
the user if they really want to switch to disabled - saying that reversing
the change is not going to work.

I thought I would ask here if the process is actually possible?