Bend in stack allowed?

[Brian.spinks]

Hoping a knowledgeable plumber can help me out. I have two issues on my self-build. Well more than two issues including running out of money! 1. The base of the stack is in the wrong position. I can correct it by using two 45 degree bends directly on top of the rest bend to offset it by 100mm which will bring it into the correct position within the studwall. I know bends in the stack are frowned upon. Should I break out the concrete breaker (150mm reinforced concrete) and move the restbend into the correct position or do you think the offset is acceptable?
2. The client (wife) changed her mind and now wants a wetroom in the downstairs toilet. The problem is that the shower drain will not meet the minimum requirement of 450mm vertical distance from the centre-line bottom of the stack. The distance is 300mm. Is this acceptable for a 40mm connection or should I use a shower drain pump instead?