Basically Hunslet Old Boys and Queens got invited into the premier and Birstall Victoria, Dewsbury Moor and Ossett Trinity into the new Championship because Yorkshire League premier became unworkable. Hunslet Warriors rejoined NCL that year. The Yorkshire league only lasted 2 seasons after that.
I found some 2002-03 seasons the other day and there were 6 teams from Yorkshire League areas:
Crigglestone All Blacks
Anyone know which one joined first? Celtic Rooster reading?
Dudley Hill A will have been among the first to join as they were booted out of the Yorkshire League for multiple registration anomalies.
Westgate were also kicked out of the Yorkshire League.