Changing the size of a font in a spooled file which has already been created MAY be possible, but the amount of code and research necessary to perform this is very time-consuming.
You would need to use several IBM APIs to retrieve the spooled file attributes, to get the spooled file data into a User Space, to create a new spooled file with the changed attributes, and then get the data back from the user space and into the new spooled file.
I don't think that your problem is solvable in that way. You are probably having problems because the driver that communicates between the OS/400 spooled file and the EPSON printer is not capable of translating the IPDS printer data stream into something that the EPSON printer can work with flexibly. A lot depends on where the driver is (iSeries, IFS, PC through Client Access, or other), the type of printer, the type of spooled file output (AFP, IPDS), the device type (*SCS or other) and so on....
Where I work we use IBM printers, which are supported by the iSeries so we don't get so many problems with printed format. I am unused to dealing with problems with other printers. But I suspect that changing the device type or the data stream type might be more helpful to you than changing the spooled file attributes.
I was thinking of creating a utility to change spool file attributes such as font, pitch, size etc., but looking at the amount of work involved I have shelved this project until I retire and have more time to do it!
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