ServiceNow kbpocalypse: This script will find all dictionary entries that are using 2020-01-01 as a default date, and tell you the number of impacted records.

kbpocalypse.js

/*
This script will find all dictionary entries that are using 2020-01-01 as a default date, and tell you the number of impacted records. 

To actually make changes, you will want to change the update flag to true;

*/

//change this flag to true if you want to update the dictionary entries and affected records
var update = false; 

//Update this value as yyyy-mm-dd
var newDefaultDate = "2030-01-01"; 

var gd = new GlideDate(); 
gd.setValue(newDefaultDate); 
gd.getDisplayValue();

var gdt = new GlideDate(); 
gdt.setValue(newDefaultDate+' 23:59:59'); 
gdt.getDisplayValue();


if(!update){
	gs.print("Since the update flag is false, we are not making upates to these records.");
}

var dictionaryEntry = new GlideRecord("sys_dictionary");
dictionaryEntry.addEncodedQuery("default_valueLIKE2020-01-01^active=true^internal_type=glide_date^ORinternal_type=glide_date_time");
dictionaryEntry.query();
while(dictionaryEntry.next()){
	var table = new GlideRecord(dictionaryEntry.name.toString());
	table.addEncodedQuery(dictionaryEntry.element.toString()+"ON2020-01-01@javascript:gs.dateGenerate('2020-01-01','start')@javascript:gs.dateGenerate('2020-01-01','end')");
	table.query();
	if(table.hasNext()){
		gs.print("There are "+table.getRowCount()+ " "+dictionaryEntry.name.toString()+" records with a "+dictionaryEntry.element.toString()+" date of 2020-01-01");
		if(update){
			var newDate  = dictionaryEntry.internal_type == "glide_date" ? gd.getDisplayValue() : gdt.getDisplayValue();
			while(table.next()){
				table.setValue(dictionaryEntry.element.toString(), newDate);
				table.update();
			}
		}
	} else{
		gs.print("The "+dictionaryEntry.name.toString()+" table still has this default value, but doesn't have any records.");
	}

	if(update){
		dictionaryEntry.default_value = dictionaryEntry.default_value.replace(/2020-01-01/gi, newDefaultDate);
		dictionaryEntry.update();
	}
}