LlListInsertList

De DigiWiki.

list numbers = [3, "three", 2, "two", 1, "one"];
default
{
    state_entry()
    {
        llOwnerSay(llDumpList2String(numbers, ","));
        // Object: 3,three,2,two,1,one
        integer index = llListFindList(numbers, [2]);
        if (index != -1)
        {
            numbers = llListInsertList(numbers, [2.5, "two and a half"], index);
            llOwnerSay(llDumpList2String(numbers, ","));
            // Object: 3,three,2.500000,two and a half,2,two,1,one
        }
    }
}

Bear in mind that the source list will remain unchanged. Instead, a new list will be produced. So, it's important that you capture this with a variable (unless you are acting directly on the results.)

Tip! To insert something at the start of a list, you can just add the two lists (putting the list with the new item(s) first)

list oldList = ["B", "C", "D"];
list newItem = ["A"];
list newlist = newItem + oldList;