This question is actually similar to another question I had asked, but this is more a response question, since I am limited to only one question per topic. SO PLEASE READ THIS FULLY.
"Using replace function to replace value to one of value map using QGIS field calculator?."
Also this problem I underfound is not related to the situation I asked that question in. The problem is that the replace function also changes the text that is has in "common" of the field value I want to replace.
I discovered a new problem with the replace function and that is it also changes the text of value's that is "common text".
Let say I have I want to change the text '2015', '2016' and '2017' to 'n.v.t.'. This works great with the replace function, however there is another text called VJ2015. When I execute the 2015 replace command it also changes this to 'vjNULL'. Again not what I want, since I only wanted that "specefic text value" to be changed not the text that is "common" with other value's. So here is my case expresion':
replace("VJ/NJ (LC)", '2013' and '2014' and '2015', NULL)
I know that programs like Excel and others have "Identical letter option", I suspect that there is a way for QGIS to turn this option on.
I also understand that "" stands for column and '' stands for the value, so I suspect I need to type some specific special character to "Indenitical on" but I do not know which. So what do I need to do?