I recently startet listening to melodic hardcore, bands like More than life, Ruiner, Napoleon.I was wondering if you guys have some tips or guides on how to create melodic hardcore songs, which scales, modes, and techniques to use,ect. or what lessons would you recommend for me, beside trying to learn to play their songs.
1) Scales and modes are largely unimportant. You're not going to be able to play "X, Y, Z scales" and "A, B, C modes" and automatically be playing something that melodic hardcore bands tend to use. So, stop worrying about that.

2) Techniques...well, the easiest way to figure that out is TO LEARN THEIR SONGS. Then, after you have learned their songs, analyze them. See what "works", what "doesn't work". Find things you liked or disliked. If you want to learn how to write in a certain genre style, then you need to know that genre.