More than likely!
Although Cradley Heath were also blocked from bringing in a lower average rider in 1979 (Teromaa for Bastable), because it still left them over the point limit, which was 50 by then.
At some point after that, it was allowed to make a change as long as the rider coming in had a lower average, even if that change still left you above the limit (i.e. the rule that has stayed in place to this day).
I've never completely understood how the 1977 points limit worked. I think it was based on start of season averages rather than how they developed across the season. By 1979, it was current averages and several teams ran squad systems at the start of the season to manipulate a way around the 50 point limit!