No. Once you contribute to a Roth 401(k), either as an original contribution or by In-plan Roth Rollover, the money and the earnings on that money are forever Roth. Recharacterization of money in a Roth 401(k) is not permitted. Rolling Roth 401(k) money over to a Roth IRA doesn't change anything.
Recharacterizations are only permitted on original contributions to a traditional IRA, original contributions to a Roth IRA, Roth conversions from a traditional IRA, or rollovers from a traditional 401(k) or similar traditional qualified retirement account to a Roth IRA. The last two are not permitted for tax years after 2017.
