Enabling TRIM much later after purchase

It should not be a problem enabling TRIM at any time. As I said, it is just a way for the file system to tell the SSD there are additional blocks that can be pre-cleaned for future writes.

When I enabled TRIM for my iMac with a 480GB OWC SSD, I used "sudo trimforce enable"

When I enabled TRIM for my MacBook Pro with 1TB Samsung 840, I used "sudo trimforce enable"

The only TRIM problem I have ever hear of had to do with Linux and using queued TRIM entires. macOS does not use this form of TRIM, and I have not heard of anyone complaining about TRIM doing anything to their 3rd party SSD's.

But having a backup, and keeping it current until you are comfortable, would be a good idea.

There have been reports here of enabling TRIM on third party Drives causing a unexpected delay in the boot up process on otherwise fast SSD boot times. Once the machine is booted—no further issues reported.

The only problems I have encountered is running TRIM on a OWC SSD, disabling it (to test the boot delay issue resolves it self) , and re-enabling for a short period to test the boot delay, and subsequently disabling it again This seem to mess with files not opening, wrong files opening, all App icons on the Dock disappearing to ? marks, Apps no longer launching. A real mess.

As stated above—always have a a current back up plan in place. How to create a boot clone

No. TRIM is a way for the file system to report which blocks of a deleted file are available may be cleaned by the SSD.

Without TRIM, any deleted files are just sitting on a file system free list, but to the SSD they still look like they have data in them. Without TRIM, those blocks do not get cleaned until the file system decided to take them off the free list and use them as storage for a new file.

Enabling TRIM now, will just start to give the SSD more blocks to have pre-cleaned so they are ready to be written. Eventually the file system will work it way through its free list and more and more blocks will get pre-cleaned.

You need to consult Crucial and Samsung to determine if Apple's TRIM command will not damage your drives.

Apple never enabled it by default because they do not test every SSD. When you use trimforce, you are taking responsibility for ensuring it will not damage your SSD.