Kinda. To the degree that the object of increase is also a percentage the statement “increasing X (where x is quantified as a pct) by Y %” could mean that X of 20% is increased to 70% or to 30%. It would be more clear to state “X increases from Y% to Z%.”
No, not kinda. In the example you present, if 20% increased to 70% the appropriate description is either a 250% increase or a 50pp ("percentage point"[0]) increase.
