Is there a tool to convert SVG line paths from absolute to relative?

In settings, under "SVG Output", set "Path string format" to "Absolute" and save as plain SVG. You may have to nudge the object so Inkskape will reset the 'd' attribute for the path.

For who's still searching for this tool. There is one made by Lea Verou on codepen that convert paths to relative or absolute.

Example convert this:

M233.51,56.8c-0.57,0.24-1.33,0.52-2.28,0.86c-0.95,0.33-1.93,0.5-2.92,0.5s-1.84-0.27-2.53-0.82
c-0.69-0.55-1.03-1.49-1.03-2.82V36.25h7.85V28.9h-7.85V16.77h-9.56V28.9h-17.84V16.77h-9.56V28.9h-4.92v7.35h4.92v21.48
c0,1.67,0.26,3.08,0.79,4.25c0.52,1.17,1.22,2.12,2.1,2.85c0.88,0.74,1.9,1.27,3.07,1.61c1.16,0.33,2.41,0.5,3.75,0.5
c2.05,0,4-0.28,5.85-0.86c1.86-0.57,3.42-1.14,4.71-1.71l-1.93-7.56c-0.57,0.24-1.33,0.52-2.28,0.86c-0.95,0.33-1.93,0.5-2.92,0.5
c-1,0-1.84-0.27-2.53-0.82c-0.69-0.55-1.03-1.49-1.03-2.82V36.25h17.84v21.48c0,1.67,0.26,3.08,0.79,4.25
c0.52,1.17,1.22,2.12,2.1,2.85c0.88,0.74,1.9,1.27,3.07,1.61c1.16,0.33,2.41,0.5,3.75,0.5c2.05,0,4-0.28,5.85-0.86
c1.86-0.57,3.42-1.14,4.71-1.71L233.51,56.

Into this:

M233.51,56.8c-0.57,0.24,-1.33,0.52,-2.28,0.86c-0.95,0.33,-1.93,0.5,-2.92,0.5s-1.84,-0.27,-2.53,-0.82c-0.69,-0.55,-1.03,-1.49,-1.03,-2.82v-18.27h7.85v-7.35h-7.85v-12.13h-9.56v12.13h-17.84v-12.13h-9.56v12.13h-4.92v7.35h4.92v21.48c0,1.67,0.26,3.08,0.79,4.25c0.52,1.17,1.22,2.12,2.1,2.85c0.88,0.74,1.9,1.27,3.07,1.61c1.16,0.33,2.41,0.5,3.75,0.5c2.05,0,4,-0.28,5.85,-0.86c1.86,-0.57,3.42,-1.14,4.71,-1.71l-1.93,-7.56c-0.57,0.24,-1.33,0.52,-2.28,0.86c-0.95,0.33,-1.93,0.5,-2.92,0.5c-1,0,-1.84,-0.27,-2.53,-0.82c-0.69,-0.55,-1.03,-1.49,-1.03,-2.82v-18.28h17.84v21.48c0,1.67,0.26,3.08,0.79,4.25c0.52,1.17,1.22,2.12,2.1,2.85c0.88,0.74,1.9,1.27,3.07,1.61c1.16,0.33,2.41,0.5,3.75,0.5c2.05,0,4,-0.28,5.85,-0.86c1.86,-0.57,3.42,-1.14,4.71,-1.71l-1.97,-7.57z

https://codepen.io/leaverou/pen/RmwzKv

Found a tool called Inkscape which allows saving to relative.

To do this:

1. New document, create a random pencil path, and save the SVG. Close inkscape.
2. Edit saved file in a text editor. Find and replace the pencil path with your path
3. Re-open the document in Inkscape. Locate and move your path. Save.
4. Edit the file again and look for the new relative path.

TADA

1. Open Inkscape and select File, Inkscape Preferences (or Shift + Ctrl + P)

2. Select SVG output

3. In the path data section untick Allow relative coordinates or select always use absolute coordinates depending on your version of Inkscape.

   This will only affect newly created paths or existing objects for which a rewrite of the path data is triggered. For existing paths:

4. Select Edit, then Select All in All Layers.

5. Use the arrow key to nudge the selection (e.g. one step up and one back down again). This will trigger a rewrite of the path data in d which will follow the changed preferences for absolute path values.

This works for Inkscape 0.48