vecor/list INSERT or UPDATE

SQL Gurus,

I want to update a specific set of rows in a column with a list or
vector. Something like,

UPDATE some_table SET col = [1 2 3 4 5]
WHERE some_condition_limits_to_five_rows;

but all I see UPDATE accepting is a scalar ("5") not a vector or list
("1 2 3 4 5")...is this even possible?

Thanks,
Adam

---
Here's a clearer (hopefully) but longer example

RPGSL_ROW_NUMBER SOME_VARIABLE

4 12
5 13
6 14
7 14
8 14

SOME_VARIABLE to be replaced with 1:5 using UPDATE so that we get

RPGSL_ROW_NUMBER SOME_VARIABLE

4 1
5 2
6 3
7 4
8 5

Adam