How to add an alias in filebeat template aliases field without distributing the other alias in aliases

How to add an alias in filebeat template aliases field without distributing the other alias in aliases

I have existing alias in template aliases. I want to add one/few allies in the existing aliases-filed of the template. How can I achieve this?

For Example

GET _tempalte/xyz
{
...
...
"aliases" : {
"a" : {
"filter" : {
"term" : {
"event.category" : "me"
}
}
}
}

After adding another alias named "b" it should look like as below

GET _tempalte/xyz
{
...
...
"aliases" : {
"a" : {
"filter" : {
"term" : {
"event.category" : "me"
}
}
},
"b" : {
"filter" : {
"term" : {
"event.category" : "you"
}
}
}
}

How can I achieve this?