grumpy and phantomotap,
as i stated - finally Excel way will be used, so it is little hard to me to understand Your offensive feelings.
Anyway - let use case to ask - excluding Excel- what alternative ways for problem, described in first post, can You propose?
I find it distasteful (I'm being really kind.) when newbies say "I'm going to do things my way because this is really just a style issue." when the reality is closer to "I'm going to do things my way because... LOOK SAND!".
The point to what everyone is saying has nothing to do with "Excel" and everything to do with processing the file on demand when the situation calls for it.
In other words, doing the job of making the data presentable should only been done when that data needs to be presented.
You are using "Excel" to do the processing. That is a simple convenience that was suggested because you said you were already using "Excel".
The simple, easy, and inescapable fact is: you can always write a small program to reverse a file on a per line basis.
It is a trivial program to code. Heck, many operating systems provide tools that can do this from the command line.
Anyway, that simple fact alone means that any logging should be done on a strict append basis. It is easy. (You only need to open the file in text mode with the append flag.) It is fast. (Strangely enough, most file systems are really good at appending data.)