HTA (Jscript) fast loading and unloading data from txt?

Question

Windows

The technology is old, but it's the only one available, an HTA application in Jscript (windows). There is a text file that is processed by a Jscript script. On small txt files, everything is fine, because The logic of the script is as follows - load an array of objects from a txt file, then process them (for example, change property values, calculate something) and then save the already updated array of objects line by line back to a txt file. The trouble is that if the file is large (more than 20 thousand years), then the HTA application noticeably starts to slow down, and the application is located on a shared disk.
I was looking for opportunities in the FileSystemObject itself by type to change only a specific line of this text file in the file, but I did not find anything, this ActiveX can either read the file line by line or completely rewrite the file.
I tried other ActiveX, for example, instead of a txt file, use Excel.Application, but it got even worse. Of the technologies, ADODB and MS Access are still available, but even here the situation is no better. What do you advise?