Your mileage may vary or do so at your own risk, whatever. Look at the Caliban definition of a detachable mag:
SENATE BILL (SB) 23
Chapter 12.8
Department of Justice Regulations for Assault Weapons and Large
Capacity Magazines
Article 1. General
978.10 Title and Scope
This chapter shall be known as the "Department of Justice Regulations
for Assault Weapons and Large Capacity Magazines," may be cited as
such and are referred to herein as "these regulations." The
provisions of these regulations shall apply to assault weapons as
defined in Penal Code section 12276.1 and as specified pursuant to
Penal Code section 12276.5, and large capacity magazines as defined
in Penal Code section 12020(c)(25). These regulations do not apply to
assault weapons as defined in Penal Code section 12276.
NOTE: Authority cited: Sections 12079, 12276.5(i) and 12285, Penal
Code. Reference: Sections 12020, 12079, 12276.1, 12276.5, and 12285,
Penal Code.
Article 2. Definitions of Terms Used to Identify Assault Weapons
978.20 Definitions
The following definitions apply to terms used in the identification
of assault weapons pursuant to Penal Code section 12276.1:
(a) "detachable magazine" means any ammunition feeding device
that can be removed readily from the firearm with neither disassembly
of the firearm action nor use of a tool being required. A bullet or
ammunition cartridge is considered a tool. Ammunition feeding device
includes any belted or linked ammunition, but does not include clips,
en bloc clips, or stripper clips that load cartridges into the
magazine.
NOTE: Authority cited: Section 12276.5(i), Penal Code. Reference:
Sections 12276.1, 12280, and 12285, Penal Code.
So if you modify the mag release and use a 10 round or less mag you no longer have an AW. But then this is not legal advise and I'm not a lawyer.