DISCLAIMER: My situation is apples to this post's orange installation software issue. But the post helped me so...
I had to register and reply for this situation because you ALL are correct here. You should NOT need to stop the system and yet the answer provided by veepee78 solves an issue -- one I had as well.
My company uses avast Server Edition and love it. I needed to change the email address that receives virus database update notifications. I couldn't make the change in the control panel and enhanced control panel. (I tried. I clicked Alerts > SMTP among other options to get to that address to no avail. Clicking the SMTP button in the Alerts tab does nothing. Perhaps it shouldn't. You certainly can provide a different solution. I don't mind a better way.) Anyway, I've heard I could uninstall/reinstall avast in order to update this entry. Didn't like that option nor believed it was the only option. Found several posts on here dictating where the avast4.ini file exists and its many tokens. Tried to edit the SMTPLogTo token and hit save but the file was in use. (Duh!) I tried to stop the providers and save: same issue. Lurked more in the forums and found a post where someone suggested to stop all services in the MMC Services panel. I did and found that the aswDisp.exe file was still open and that I could not stop it in the Task Manager. "Access Denied!" Fair enough.
Enter this post. I agree with you that avast need not be stopped. But I still needed an answer to help find a logical solution and relay the message here for future development purposes, if any. So I followed veepee78's one-step solution (with all services stopped) and it didn't work. But heck, nothing worked when I stopped the services in services.msc. (This is where the evangelists and tech support are correct. You shouldn't need to stop it and stopping it may cause more factors.) So I started the services back up and un-did veepee78's solution. The avast4.ini file is still in use and I'm still out of luck. Lastly, I re-instated veepee78's solution (which is an avast feature, meaning it was put in there for a reason by the devs). I could save the file. Success! Of course, I unchecked the checkbox right afterwards to be sure.
After that, I tried one more time to make an edit to the ini file and hit save. Once again, file was in use. So that completes my observation. I hope that helps others and that the responders in the forum keep providing solutions regardless of conflict. Conflict brings correction through compassion and compromise.
The quick and dirty...
1) You should NOT need to stop the services for any reason. You may have to stop the providers on extreme cases.
2) You can check the "Disable avast! self-defense module" in the Troubleshooting section of Settings... on extreme cases. But this is a troubleshooting "feature" that should be unchecked after you evaluate your situation.
3) When all else fails, the tech support, evangelists, and community are not the enemy. Try to post your issues (and responses) without slander, sarcasm, or the like. All thought should be welcome if it is removed of commentary. Otherwise, it only expands the thread with many tangents.