Hi and welcome!
I would rather suggest importing the selections from a text file, as you can specify both their names and the odds at which you want to bet.
You place the name of each horse and its odds on a separate line, with a tab character in between, e.g.
Horse1 5.5
Once you've imported such file, the program will match the names in it with the selections in My Markets, and will disable those that are not in the file.
Later you can just use the variable imported_1 to make a bet at the set price, as this variable refers to the value that stands next to the name in the file.
I should really make an example on this. Meanwhile please read chapter "Triggered Betting - Reference - Variables - Selection Variables - Variables referring to imported values" in the manual.