jQuery Grid Plugin - jqGrid

According to doc:

succesfunc: if defined, this function is called immediately after the request is successful. To this function is passed the data returned from the server. Depending on the data from server this function should return true or false.

But when I return false from succesfunc, I expect the row being edited remain intact with user changes

e.g. I call editRow on dbl-click and pass my succesfunc, on successfun if there are any problem reported in server data, I show error to user but do not want that row being edited is closed with user modifcations gone.

So I return false from succesfunc, but it still closes the row.

Looking into code confirms the behaviour

in grid.inlineedit.js

if (ret===true) {
….
} else { $($t).restoreRow(rowid); }

What is the easiest way to tweak this? If make a change on my side, how do I minimize it? I do not have much exp. with java script.