no its not possible ootb in 2010, your talking about changing the identifier column. its easy todo but would require coding tho!
it will get messy quickly! say you have
1 , 2 , 3 , 4 and you removed 2 so you now have 1 , 3 , 4 . you would need to not only change 3 to 2 but anything after it down a notch!
you can do this in code using the item deleting and deleted. passing the value of the last ID and moving it along to the next row instead.
for continuity you should keep the ID column as is, create a new column
/// An item was deleted.
public override void ItemDeleted(SPItemEventProperties properties)
//start the ID count at 1
int i = 1;
int paletteInt = 1;
//need to loop through each item in the whole custom list
foreach (SPListItem itm in SPContext.Current.Web.Lists["MyCustomList"].Items)
//as we are going through each item the ID should match our custom ID column. If not update with the correct ID
if ((int)itm["myID"] != i)
//update your custom column ID with the new matched ID
itm["myID"] = i;
//check every third number of i int, if it is then update the paletteInt number by one
if (i % 3 == 0)
//update the item after the above has run
itm["palette"] = paletteInt;
//increment the ID on each loop