I'm working on adding tools to this site.
If I can achieve it, there should be a place where you can fix subtitles index. I'll keep you informed.

If you need to insert lines, or do anything else in a .srt file that you can't do on your mobile device, you can email it to me, I'll add the lines wherever you want using Aegisub, and I'll send it back to you. No problem for me.

Thank you Nochvemo, I'll keep that in mind, but it's working out fine for now.

In reply to truc1979:

I'm working on adding tools to this site.
If I can achieve it, there should be a place where you can fix subtitles index. I'll keep you informed.

I would suggest you save your time for more important things. Adding lines using high numbers is easy and you can add as many as you like. Just don't duplicate line numbers.

Don't worry, I'm not working on a tool to fix your issues :)
I'm working on more global subtitles tools for translations (and sync), but these tools don't keep indexes provided: they re-number them (so it could be another solution for you)