My fissure happened about a year and a half ago and I'd say for the past 6 months I've been okay with bowel movements (as long as they are soft), but I have a permanent soreness/tender pain that makes it difficult to sit down or even stand up for long periods of time.

I can feel a long rigid line right at the 6 o'clock position (back) where the soreness is coming from, and it feels like scar tissue.

It's going to take ages to actually get an appointment with a CRS, so in the meantime what is there to do? Would applying heat or cold directly onto the scar tissue do anything?

I have the same problem of painful scar tissue. I also have some nerve damage in the area. I think for most people it just gets better with alot of time. I put a tiny bit of barrier cream on my anus to protect from irritation, as I find that if I do alot of walking it rubs and irritates things further. Heat or cold can help ease the discomfort too.
My pain was so bad I have resorted to gabapentin... It is a nerve pain drug. I am on a low dose.... But it has helped to take the edge off.

OMB

I have scar tissue from LIS and fissurectomy which can be felt like a long ridged line inside the rectum, I believe this is what causes most of my pain these days.

I have really bad flare ups of intense agonising rectal pain and think the scar tissue gets inflamed during/after defaecation.