Different block deltas in different module versions

Problem/Motivation

Style Switcher 6.x-1.x has numeric (0) block delta.
Style Switcher 7.x-1.x and 7.x-2.x have word (styleswitcher) block delta.

So when upgrading from 6 to 7 the style switcher block disappears with all its configuration, and site admin has to configure it anew.

Proposed resolution

Implement hook_update_N where update block delta using update_fix_d7_block_deltas() function.