First let us reference a more common discussion among poskim, which seems to be almost identical. Then we can see how to apply the conclusions to your question.
The Pitchei Teshuva[1] discusses the case of one who removes a mezuza to check if it is still kosher. His first thought and that of other Acharonim (we do not find sources among the Rishonim) is to compare this question to an even more well-known one. The Tur[2] says that if one removes his tallit with the intention of putting it back on after a relatively short amount of time, he does not make a beracha when he puts it back on. The Beit Yosef[3] disagrees based on a gemara[4] that relates that Rava would make a beracha on his tefillin every time he returned from the bathroom, despite the fact that he had intended to put the tefillin back on immediately afterward. The Darchei Moshe[5] deflects this proof by distinguishing between the cases based on the nature of the break. When one enters a bathroom, he is not allowed to wear tefillin, so the resulting break is a major interruption. In contrast, one who removes a tallit can put in on again at any time, even in the bathroom. The Shulchan Aruch,[6] based on his comments in Beit Yosef, requires a beracha when putting a tallit on again. The Rama[7] (=Darchei Moshe) says not to make the beracha.
The Admat Kodesh[8] says that those who follow the view of the Shulchan Aruch (classically, Sephardim) should likewise make a beracha when putting back a mezuza, as the mitzva was interrupted when he removed it, whereas those who follow the Rama (Ashkenazim) might not. However, on the tallit issue itself, later Sephardic poskim rejected the Shulchan Aruch’s view and do not require a beracha upon returning a tallit.[9]
The assumed connection between tallit and mezuza is also questionable. One of the most authoritative Sephardic poskim, the Chida, writes[10] that after removing a mezuza to check it, it is possible that one should make a beracha upon reaffixing it. The Pitchei Teshuva[11] explains that the Chida’s doubt may be based on the following distinction between the case of tallit and that of checking a mezuza. One who removes the tallit has every reason to expect that he can subsequently put it on without problem or unnecessary delay. However, when one removes the mezuza in order to check it, he should be concerned that it may be found pasul. Therefore, it is harder to say that his intention regarding the continued performance of the mitzva is uninterrupted.
Another factor that plays a role is time. The Aruch HaShulchan[12] says that if a day goes by before he puts the mezuza back, he should make a new beracha. It is difficult to summarize all of the opinions among the latter poskim. It appears, however, that the majority of poskim say that when one checks the mezuza and puts it back promptly, he does not make a new beracha. To a great degree, this is due to the concept of safek berachot l’hakel: if one is unsure whether a beracha is warranted, it is safer to refrain from making it. Notably, Rav Ovadya Yosef[13] uncharacteristically requires a beracha where most do not. A logical compromise position is that if one gives the mezuza over to a sofer to check, with the matter leaving the owner’s control, then a beracha is required, but otherwise not.[14]
When one paints doorposts, he fully expects to put the mezuzot back; thus, at first glance, one would not make a new beracha upon returning them. However, there can be a few reasons to make the beracha, according to our discussion above. Usually one leaves the mezuzot off for a couple of days so the paint will dry. It is also an opportune time to do the required, periodic check (twice in seven years). In addition, if one switches around the mezuza scrolls from different doorposts, even more opinions require a beracha (beyond our scope). If one combines all the factors, the beracha is clearly appropriate.