I see and use lot of powerful Luci elements selecting/using routing table names from /etc/iproute2/rt_tables [1] but do not see any editor of /etc/iproute2/rt_tables.
Am I blind or it is the way how it is supposed to work: first edit/add table name in /etc/iproute2/rt_tables from CLI and than use in luci ?
[1] Like Interface "Advanced settings" tab with "Override IPv4 routing table".
P.S. I am really amazed how with luci one can do just the right thing in terms of policy routing tables management!