I've successfully done a few "rewrites" but truthfully, the "rewritten code" was put into production, replacing the old code, within a month. Rewrites don't work if you have to wait to use the code.

Basically, if you plan to rewrite something, plan on getting it released to production on the same schedule that you would release everything else (maybe a month longer? but not much). If you can't do that, you cannot do the rewrite.