[KyleGoetz]

I've a new question about 並行して／た
I know 並行して as "to do something at the same time." But I realized 並行した also works. I'm curious as to whether there's a difference in usage.

Looking at samples in Eijiro, I see that
並行した生活を送る is a phrase (basically, "to lead two lives in parallel")

Would 並行して生活を送る be correct also? If not, why? If so, is there a difference in nuance?

Because I know things like 並行して実行しているプロセス are correct usages as well, but this time it's して instead of した.

And that's not to mention the option of dropping する altogether and saying something like 並行イベント or using の and saying 並行のイベント, but those I have less a problem with dealing with since I know sometimes you can drop the linking の and basically it just makes the phrase sound slightly more "official" or something more formal (??) in tone.

My best guess is that 並行して would be used when you're talking about two things happening at the same time, but 並行した would be used when you're specifically talking about one of the things that is happening.

So in the first example, you're talking about a second 生活 that is being lived, so 並行した is correct. However, were you saying that a person has two lives, 並行して would be correct.

So in that case, "this is the second process, which we run simultaneously" might be これは並行したプロセス..., but "we run two processes simultaneously" would be 並行してプロセス...

But even as I type that, I think that's a weird, super-nitpicky attempt at drawing a distinction that actually doesn't exist.