Exempting a cell containing a specific character

First, let me clarify that this is my first time doing anything with Google Apps Script or javascript in general. I'm trying to create a function that adds checkboxes to all cells in a column which is easy enough and I've already managed this.

I do, however, have a caveat:

• I press the button I've assigned my function to and it applies a checkbox to every cell in the desired row.
• I want to create an exception to this function for all cells containing a certain character (in this case, "¬".)

function addLine () {SpreadsheetApp.getActive().getSheetByName("RP Checklist")    .getRange('A5:A')    .insertCheckboxes();}

This is what I have so far. How would I go about creating the desired exempt cells?