I want a skill code to change the mos parameter of length

You could try to address the root cause first. The most likely scenario is that callbacks are triggered and re-evaluating the length based upon another parameter (although this is surprising; I would expect length to be a primary attribute and other parameters might be dependant upon it). So one way to check would be disabling 'Trigger CDF callbacks' on hte Spince In form. The default  is 'on' like this...

Turn it of.

Alternatively you can use the Edit -> Replace form: Search for 'other' and enter the length parameter name (probably l) == 0.3 replace with 0.4. Apply, Replace All.

Again, consider dependant parameters. Callbacks might need triggering. See...

How to call CDF callbacks procedurally from SKILL to update CDF parameters?

Now schematic Spice Import already done.

I don not want re-import.So I want a skill to modify the length.0.3um to0.4um

Thanks.

As I suggested: You can use the Edit -> Replace functionality. SKILL not necessarily required.

If you prefer SKILL this might help...

How can I change or modify or update instance CDF parameters and properties in a schematic using SKILL

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ok,I try it.

but thi website I can not open. I don not know Why? view this warning

I’m dealing with a schematic where spiceIn changed all MOS device lengths from 0.4um to 0.3um without error. Now I need to revert all of them back to 0.4um. There are 215,885 MOS types in one cell.