This is one of the reasons I use sumps for filtration, if I want to set up another tank, I attach it to the seasoned sump, and it is automatically cycled because the seasoned media in the sump is what is being used, and will easily handle the extra fish and water.
I just picked up another tank, and as soon as the plumbing is up and running, I will add fish, no need to cycle.
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I will just reroute the outflow from the large tank on the left thru the empty one on the right, into the sump you can see behind.
Until I moved, using seasoned sumps, I hadn't had to cycle since the 80s.