Doctype + naming series issues

i have created a doctype with a naming series
.XXX..IMP.ADV..YYYY
.XXX..IMP.OAA..YYYY

Entered some data and submitted the records …
But when i changed the naming series to
.IMP.ADV…YYYY
.IMP.OAA…YYYY

And when tring to enter new records the select does not bring the new changes but the old ones … i have clear-cache and restarted and still … so i have tried to use the Naming Series with the new changes and when adding those
.IMP.ADV…YYYY
.IMP.OAA…YYYY

It returns the below message

Special Characters except “-”, “#”, “.” and “/” not allowed in naming series

Now have those two issues:
Why not accepting the new change and why the error message on the Naming series?

“why the error message on the Naming series”

For answers best to check the code -

frappe@erpnext:~/frappe-bench$ find . -name '*.py' | xargs grep 'Special Characters except "-", "#", "." and "/" not allowed in naming series'
./apps/erpnext/erpnext/setup/doctype/naming_series/naming_series.py:			throw(_('Special Characters except "-", "#", "." and "/" not allowed in naming series'))

and here too

“Why not accepting the new change”

Because saving the change does not update or replace the original naming_series spec stored in the db.

To effect the change you require, one way is do that in the db but take care if that is a production environment.