I recently left my employer, with whom I had a 401k account. For the year to date date, I had some post- and some pre-tax contributions to that account coming out of my pay. Since my new employer does not have a 401k, I will make no more 401k contributions this year. Can I reclaim the tax I paid on the post-tax contributions in some way ( tax deduction / credit ), since the total will not surpass the maximum pre-tax contribution for the year?
You are asking if you can, in effect, deposit pretax dollars to the 401(k) after the fact. I don't believe that's possible. You've already separated from that employer.
I am not even sure that you could re-characterize them after the fact, even if you were still employed with them. I am sure there is a procure for re-characterizing funds if they were mistakenly deposited the wrong way, but that is not your situation.
You are asking to un-Roth the funds. Most people are more interested in converting non-Roth (401K or IRA) to a Roth account. In fact the general advice is to deposit enough 401K funds to get the full match, then deposit funds in a Roth IRA, and then put the rest in the 401K up to the yearly max.
Because you had a 401K for part of this year, the IRS limits the deductability of IRA funds for 2013. You new IRA deposits are likely going to be of the Roth variety.