Let's say we have a list:
`listA = ['stack', 'overflow', '1', '2', '3', '4', '1', '5', '3', '7', '2', '3', 'L', '1', ..., 'a', '23', 'Q', '1']`

I want to create a new list such as:
`new_list = ['1234', '1537', '23L1', ..., 'a23Q1']`

So, in this case I want to create a new list using "listA" by removing first two elements and merging all next elements in groups of 4, so the elements: 1, 2, 3, 4; are one element now.

How to approach this in case that I have a very long list to modify. Also, would be nice to know how to approach this problem in case I don't need to create a new list, if all I want is just to modify the list I already have (such as: `listA = ['1234', '1537', '23L1', ..., 'a23Q1']`). Thanks.