Some people core aerate in order to expose more soil and improve the seed-to-soil contact. Others have had problems as a result of aerating because it brings weed seeds to the surface. A soil test is a good thing, but to really make use of it, you need to be able to interpret the results. The best time to overseed is after the summer heat breaks and when you can be around enough to ensure that it gets watered enough to stay moist until the seeds have germinated.

It can be used as material for a compost pile, but with the huge amount of seeds likely in it would not make for good mulch.

Thanks a lot for all the responses. I have purchased the rye grass seed and I will overseed it very soon. I am concerned about weakening the existing grass, but I just have to try and see this year and decide whether it is better to have the bermuda weakened or to put up with brown grass half of the year. :) Anyway, before I go ahead, I have some final questions in my mind: #1 Here is the current state of my lawn. It is not completely dormant I guess, but almost. Do you think it is better to wait a bit more so that it goes completely dormant, or should I overseed it right now? The weather is expected to be around high 60's (F), max 70F during the day and mid 50's (F), minimum 53- 54 (F) during the night until the end of October. #2 The place that I purchased the seed advised me to apply the seed at a rate of 30 g. per square meters (approx. 6.5 lb per 1000 sq. feet). Is this a good amount? #3 After I overseed, I know I have to water frequently, but refrain from creating a pond on top. Here, the soil is always wet now in the mornings because of the dew, so I suppose, watering early in the morning and at night isn't necessary? Is once midday and once early in the evening with the sprinkler system sufficient? #4 I believe my current grass is not common bermuda, but a variety instead (more dense and thinner and finer looking blades). Is it possible to identify it? Here are two more closer pictures:

2 year update! The Turf Blue bluegrass has adapted very well to the NC environment. Disease has not been an issue - which is refreshing, and the cultivars in the mix are very aggressive - they filled in 6" holes left over from dead Bermuda in 6 weeks. The relationship with this mix has been a bumpy one. There have been periods when the grass looked lime green and I've seriously considered nuking it, but the fact it's so resilient stopped me. Meanwhile, I've learned to work with it, and it with me. I've learned that cutting below 2.5" produces some sort of reaction in the grass and it starts to put out massive amounts of new lime-green growth. As soon as I stopped trying to go lower and stabilized the HOC at 2.5", the color issue went away. Also, color has improved with age. And finally, PGR and FAS bump up the color significantly as well, bringing it into the acceptable range for my taste. Drought tolerance is similar to fescue, maybe slightly less. However, recovery from dormancy is outstanding, so even if it browns a little, it comes back with a vengeance. And where it doesn't, it spreads to fill in. It's peace of mind, and it's priceless. Because I know I can afford to push it and let go a little brown, I probably used less water on this summer that I used to use on fescue. Disease has not been an issue, brown patch doesn't touch it. So, I'm going into my 3rd years with the HGT mix. I am very pleased with its performance, and I expect even better now that it's mature. Color can be successfully managed, and it lives up to the H in HGT. Highly recommended as an alternative to fescue for the Transition Zone. http://lawniac.com/wp-content/uploads/2018/11/lawn_oct_2018.jpg