I doubt that that would be desirable, as competition,product design, meeting policyholder's reasonable expectations, etc are still desirable.
Assets should still match liabilities, so investing in cash primarily because of the low return and implications on the tax position would not be such a good idea (unless of course cash is the best match).
It also depends on how a company allowed for tax in it's pricing basis. If it assumes that it's Investment Income will exceed Expenses and then nets down Expenses in the pricing basis, when in fact I-E turns out to be <0 (due to for example investing in cash), then it won't get the relief on expenses as assumed in the pricing basis, which will affect profits.