This lawncare product is a 3-in-1 solution containing seed, fertilizer, and soil improver. Can I use an overseed machine with the fertilizer and soil improver mixed in or will that harm the machine since those additions are not shaped like a grass seed?
I am assuming you have cool season lawn grasses. Thatch is not a problem with 365 days of warmth for decomposition.
Overseeding is not a regular, normal process for lawns...cool season lawns. Without proper preparation, the correct seed mix, being able to water tiny areas within a huge body of lawn...seed needs a consistently just so moist soil or forget germination. That means watering when ever that surface soil dries out, sometimes up to 7 times per day in hot weather and bright sun.
This weird specialized watering for your SPOTS lasts until you are able to do the virgin mow. Then you use that grass, the newbie grass to tell you when to water again until all of that grass is on the same schedule, all with deep roots and NEVER having less than 3 inches of top growth. Below that length, the grass gets stressed. Genetically gifted I guess with huge root systems, those root systems need the top growth to FEED those roots or that grass plant is stressed and fragile. Allows weeds to insert themselves.
I haven't used, probably will never use a 3 in 1 product for overseeding. Just trying to tell you I've never seen the need for overseeding much less invest in overseeding.
I would most certainly ask for estimates from your local grass companies. Free. Might even make sense for your pocket book. Remember, grass seed or sod companies have to be successful to continue business. They would be very into teaching you how to grow this monster the lawn so they don't have to do a call back.
So sorry I am not answering your question. I just am able to know there is more to this story and this problem that I could help fix, help you understand. I do not think you should mess with this machine. Spraying grass seed, fertilizer, soil improvement stuff from a machine does not ensure a thicker grass. I've never found overseeding to help at all. If a lawn isn't thick and lush there is something going on that has to be addressed. Overseeding is not a regular part of lawn maintenance. A thin lawn needs to be diagnosed first. Overseeding is rarely a fix.
There is nothing one can spray on soil to improve it.
Adding fertilizer to newly germinating seed is contraindicated.