HOW to configure Xournal to delete by stroke by default

I have been using the software Xournal extensively in the last 15 years, under various operating systems, and lately as a virtual board in class (which I export to pdf for the student after class). One very useful feature is the "delete strokes" mode of the eraser, which is not the default mode. I would like this option to be selected by default (to save 3 seconds every time I start xournal). I tried to save the option "as default" and to "save preferences" without success. Some other features DO seem to be saved and recovered from the preferences, but not this one. I tried to download the source code and to edit it, but got a bit lost in it. Is there an easy way to configure Xournal to delete by stroke by default?