Unfortunately, if it is not not compliant as it stands with the grip fin, then no. The non-compliant mags are just not sent so that would be a non issue. Here are the CA compliant rifles available on Bud's now.
budsgunshop.com/search.php/q/california+compliant+rifle

Hi Daryl, Bud does not modify or ship non-compliant firearms. You can find the CA compliant Gen 3 Sub2000 model with Grip Fin & Pinned Stock here >>> https://wbtguns.com/rifles/semi-auto-rifles/kel-tec-sub2000-gen-3-california-legal-9mm/
Stay safe & have a great day!

Hi Daryl and welcome. The Sub2000 is not CA legal even with a 10rd magazine. Some CA legal 9mm carbines here: budsgunshop.com/product_info.php/products_id/100463/hi+point+995tsca+9mm+16.5+10rd+ca+compliant --------------------------------------budsgunshop.com/product_info.php/products_id/169327/smith+%26+wesson+response+carbine+10+rnd+ca ------------------------------------------ budsgunshop.com/product_info.php/products_id/56185/ruger+pc+carbine+9mm+10+1+fluted+16+barrel ----------------------------------------------- budsgunshop.com/product_info.php/products_id/113037/ruger+-+pc+carbine+9mm+16.12+fluted+barrel+adj+ghost+ring+black+synthetic+10-rd

No.