production queue

I recently tried on UB function that allows extra specialist slot to technology buildings (public school and laboratory 1->2) What I did was creating a copy of original building with extra slot and used lua to replace the original building into specialized version when created in city. It...

... being removed from the production queue, when some amount of hammers have already been put into the obsolete unit. Example- Lets say I'm building a Slinger while researching Archery. I have put in "X" amount of production into the build. Now I start building a Builder and leave the Slinger...