How can I change the default prefix that erwin assigns to the Primary Keys, by default it appears XPK and I need to change it to PK? 

Question: How can I change the default prefix that erwin assigns to the Primary Keys, by default it appears XPK and I need to change it to PK? 

Answer: To change PK index name and remove the X from the default name, the "Index to Key Group" in the "Model Naming Options" dialog field would need to be replaced to the following macro:

%Switch(%Substr(%KeyType,1,2)) {%Choose(PK){%Substr(%KeyName,2,%Len(KeyName))} %Choose(IF){%KeyName} %Choose(AK){%KeyName} %Choose(IE){%KeyName}}

Here is the steps:
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1. Select Tools > Model Naming Options:

2. Select the Name Mapping tab:

3. Input the following in the Macro Name for Object Type: Key Group to Index:

%Switch(%Substr(%KeyType,1,2)) {%Choose(PK){%Substr(%KeyName,2,%Len(KeyName))} %Choose(IF){%KeyName} %Choose(AK){%KeyName} %Choose(IE){%KeyName}}​

4. All PK Index Names should now remove the default X prefix: