Hoping someone can help me out regarding the offset-curve filter.
Now that its applied I cannot change it or remove it?
I am new to Glyphs 
If you can’t cmd+Z and you don’t have version control, then i think your outline is lost.
For the future though, there are a couple ways you could use to avoid this.
You could keep your outline in the background of your glyph. To do that you can use cmd+J to copy your selection to the background and cmd+B To edit the background.
Another way would be to use custom parameters such as filter or preFilter to apply your filter on export only. This way you can keep all your outlines in your glyphs.
I hope I’m clear. If you need more information, you can search the handbook or you can read these tutorials:
On monoline fonts: https://www.glyphsapp.com/tutorials/monoline
On custom parameters: https://www.glyphsapp.com/tutorials/custom-parameters
Thanks Jeremie!
Let e explain what I have done, maybe you could help me improve my workflow:
I was following the monoline tutorial, and the whole creating instance for font export made perfect sense
So I wanted to test the font in edit mode by 'show preview offset’
Now the preview was showing a version of a value of 20, which didn’t look great, and the instance also had the value of 20.
So if I exported the font it wouldn’t look great.
My real question is how to change the value of the offset until I am happy with it without being stuck with it?
The monoline tutorial explains the process of adding the filter then immediately cmd+z to save it into the memory.
Once in the memory / preferences how to change the value?
So if I wanted to export the font with a offset value of 15, how could I preview it in edit mode?
I hope this makes a bit more sense of what I am trying to achieve.
Thanks
D
Ok wait before I waste your time. Let me explain what just happened now.
I followed your advice and created the background layer etc.
Applied the offset curve.
Glyphs crashed
Reopened and now I am stuck with the offset curve.
That is what is bothering me. Now how to remove it from the glyph? Its stuck with it?
Yes. If you don’t have a copy of your file…
Ok thanks Georg. I am curious though, is there maybe a technique to play with the thickness and then dedicate to the font?
Couldn’t the ‘show preview offset’ actually preview the instance and not what was previously applied as a filter?
That is what the filter does when the dialogue is open. You can step through values with your up/down arrow keys. Add the shift key for increments of 10. And you see live what’s happening.
If you apply the filter once (and immediately undo), the offset values are used for the Offset Preview (at the bottom of the View menu).