You can do the reopen on any device as many times as you want. You would do this, for example, to start a program on /dev/con1, then start the shell on /dev/con2, and then start another program on /dev/con1 again:
[+script] .script = { ... reopen /dev/con1 prog1 & reopen /dev/con2 [+session] esh & reopen /dev/con1 prog2 & ...