You can't change tech cost (API limitation) but its workaround disable research for landfill, add chest (unmainable,etc) where u will check if player has 999 packs next clear chest and enable research for landfill and set it progress to 99% (Again API limitation "the new progress must be < 100%...

@Klonan Ty for reply. I will try with checking.

Hello, I try make a tower defense scenario and i don't want to check every time when player place a structure because optimization(xD) and I need a item like transport belt, entity can go pass thru but player can't build on it. Ether I don't want make a separate mod for specify scenario because ever...