Return a value in a column

I would use this for your average calculation:

AverageWithout43568s = CALCULATE(AVERAGE('board-Query'[Generation Duration]), 'board-Query'[Generation Duration] <> 43658)

And replace the average with whatever calculation you want to do for other measures.

If you really need a calculated column that shows non-43568 values, you could edit your original formula for a calculated column:

Generation Duration 2 = IF('board-Query'[Generation Duration] = 43658, BLANK(), 'board-Query'[Generation Duration])

You could also clean that up a bit more since IF defaults to null if you don't provide an alternate value:

Generation Duration 3 = IF('board-Query'[Generation Duration] <>  43658, 'board-Query'[Generation Duration])