Help on pushing files to device (ADB) topic

Hello guys, experiencing another problem now :silly:

So I was just making a rom, which I have already installed. It's based on Cataclysm (personal use only - Till I ask for perm).
I have installed the rom, then I decided to theme some system files. And so I did. I theme the "Settings.apk" for now, and decided to push it to my device instead of installing the whole rom over again. Now mind you when I made roms and modified system apps, pushing these files to the device was straight forward. However on this Hammerhead, I've been running into some issues.

When pushing the file to my device like this

Code:

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adb push Settings.apk system/priv-app

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.
I get an error that says -

Code:

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failed to copy "Settings.apk" to "system/priv-app/Settings.apk" : Read only file system.

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So I then decided to try the following -

Code:

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[x] adb root - Permission Denied
[x] adb remount - Permission Denied

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So then I decided to use some shell commands to set the system as rw, I did the following.

Code:

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[x] adb shell
[x] $ su - gave it permission
[x] $ mount -o rw,remount /system - It mounts it.

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I then restarted cmd with root permission.

Code:

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adb root"

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- it restarted however, this time it stated.

Code:

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Device not found.

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I probably did the wrong thing above, so how exactly can I push files to /system?