Could I try and answer by taking your last point first. I read your post as saying "Eglington is PPR anyway so why publish opening times or a change in opening times because you must ring to establish PPR anyway and they will tell you". The reason for this NOTAM, I think, is because the NOTAM process is used as the update system for the UK AIP "library". Licensed airfields have an obligation to publish a set of data which, as we know, is incorporated into the UK AIP. When the data needs to be updated the NOTAM process is used. After the AIP is updated with the correction, this type of "XXXX to perm" NOTAM will be removed from the ADIMS database and will not appear in the Pre-Flight Information Bulletin (PIB).
At the moment the AIP specific airfield entry for Derry reads:
Winter
Mon-Fri 0700 - 2015 Sat 0700 - 1545 Sun 1230 - 2115 (By Arrangement)
Summer
Mon-Fri 0615 - 2015 Sat 0615 - 1545 Sun 1130 - 2015 (By Arrangement)
So effectively what they are saying is "We are updating the UK AIP and here are the new opening times"
Notwithstanding the above "official" published hours, if the ATSU has manning problems such that they cannot provide the required level of service then they have little option but to withdraw the airfield from service. Perhaps this is a short term manning problem (e.g. day-to-day) and that long term recruitment is actively underway by the ATSU concerned; I cannot comment because I don't know the detail at this airfield.
To your first point, why is it repeated. The reason is they have followed the ICAO Annexe 15 rules to the letter and submitted three NOTAM B0620/03, L0788/03 and L0789/03 because the change in these hours affects three different elements of the airfield operation which Annexe 15 required a NOTAM for; ATZ, A/D and Twr/App op hours I suspect. They could have combined these three perhaps and used a different code (XX) in the Q code. There is a good example of this and a more complete explanation
Here. Look at the paragraph half way down that starts "NOTAM Code, a 5 letter code...." Mike and Russell have explained the same issue concerning a runway lighting in the example.
Regards
Andy