First is there a standard set of escape codes I can use across all printer types? And second if not, does each maker (ie HP, Epson, brother) have their own set of codes that will work across all of their printer types?

No there is not one set of printer codes for ALL printers. Most HP printers can be set to Epson emmulation which would then allow you to use Epson escape codes. Most HP Printers use PCL codes that are rather different to Epson escape codes. You should be able to get the PCL codes from the net. Any user mannual from an Epson printer should have the escape sequences in the back.

I am using a customized software which does not allow me to change the setting of printer setting parameters. I am now using Epson LQ-300+ which allows me to change the default setting on the printer panel. But the procedure is so tedious. Is there any way to write a short program and run from the PC to change the parameter (eg font, pitch) before I use my customized software to print out?