No.
You misunderstand the concept of copyright.
If a script is published in a way that disclaims copyright [typically in the wording in its header, which puts it freely into the public domain] then you are free to do what you will with it, edit it and even republish it with changes - although doing so without making it clear it is now 'your' version could confuse others, and at least annoy the original author.
A script might be published explicitly claiming copyright [or if there is nothing said to the contrary the copyright is deemed to remain with the original publisher or author - the 'owner'].
In that case you may not change its contents and republish it, without the express consent of the 'owner'.
However, if you make some changes and use that changed file for your own private purposes then who is to know...
I suggested a simple 'tweak' to the copyrighted 'select.rb' to make it compatible with newer versions of SketchUp - it was adding a couple of lines at the start to fix an oversight by the original author, and which I an sure he would have agreed with.
If any of you then decide to try that 'tweak', it's up to you, I did NOT republish the file.
I trust you will not do so either.
I declined to make significant changes to his copyrighted GoldenGauge.rb, this is would have meant a major rewrite and posting large blocks of code - tantamount to republishing a then much edited version of the script.
I could do that for my own personal use but not post it for the rest of you, as I then consider that infringing copyright rules...
However, I did make significant changes to' LiveIvy', because the original author invited users to make changes and improve the code, effectively disclaiming any copyright he might have had.