To distinguish if the script hangs or is just processing for a long time, best add some write to console blocks which report step by step what the script is doing. Then make sure the console panel is open when you run the script and then you see the progress. Then you can understand better, what the script is doing and if is is just slow, hangs, or maybe runs in some kind of infinite loop. The "Update Texts of Ae Mort with Spreadsheet" already contains such console output, which you can enable with the "detailed console output" checkbox in the input panel.
In general, yes, the "Update Texts of Ae Mort with Spreadsheet" needs to look at all clips in the sequence, since it has no idea where the mogrts are, so it needs to look for them. If you have the clips that need to be modified, listed in the spreadsheet, then it will definitely be more effective to just loop over those. This is what the tools in the library at
Examples/Templates/Clip Property Spreadsheet
are doing.
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