Mac OS X 10.10.4, which is released on June 30, 2015 and the upcoming 10.11 “El Capitan”‎ will allow the user to enable TRIM on third party SSDs. They include a command trimforce to make this happen. If you don’t want to upgrade and still want to stick with 10.10.3. There is still a way to do it. I found a guide that showed me how to enable TRIM to on 10.10.3 to support TRIM without disabling kext signing or patching the system file IOAHCIFamily.kext by just adding one Apple signed system file AppleDataSetManagement.kext from El Capitan.

The original guide is here. I recommend the “Even Better Method (No kext-dev-mode required!)” in which you download the zip file containing the Apple signed file `AppleDataSetManagement.kext` which is new in El Capitan and unzip it in `/System/Library/Extensions`.

With that file in place, you can disable TRIM enabler and reenable kext signing again after making sure that you have the original IOAHCIFamily.kext file restored. In case you had the wrong IOAHCIFamily.kext file after enabling kext signing like me and got a block sign when booting, you can always follow Cindori’s guide to reverse changes done by trim enabling software.

Here is the screenshot of TRIM enabled on 10.10.3 with NVRAM/PRAM intact WITHOUT setting kext-dev-mode=1 to disable kext signing.