Hi partner,
You could use C# to insert new options to option set field.
1.Create a console app project and connect to Dynamics 365.
https://arunpotti.wordpress.com/2018/02/03/step-by-step-to-connect-dynamics-365-crm-online-v9-x-using-c-console-application/
https://docs.microsoft.com/en-us/powerapps/developer/common-data-service/xrm-tooling/sample-simplified-connection-quick-start
2.Add options to the option set field.
// Create a request.
InsertOptionValueRequest insertOptionValueRequest =
new InsertOptionValueRequest
{
AttributeLogicalName = "new_picklist", //field name
EntityLogicalName = Contact.EntityLogicalName,//entity name
Label = new Label("New Picklist Label", _languageCode)//label
};
// Execute the request and get the value.
int insertOptionValue = ((InsertOptionValueResponse)svc.Execute(
insertOptionValueRequest)).NewOptionValue;
Console.WriteLine("Created {0} with the value of {1}.",
insertOptionValueRequest.Label.LocalizedLabels[0].Label,
insertOptionValue);
https://docs.microsoft.com/en-us/dotnet/api/microsoft.xrm.sdk.messages.insertoptionvaluerequest?view=dynamics-general-ce-9
BTW, adding 100 options is a very heavy work and it is also not easy to find the option you want in the 100 options without searching feature.
I suggest that you could use Look up Field insead, you just need to create another new entity and build a 1:N relationship between the main entity and the new custom entity.
As you can see in the picture, yo could use filter or searching feature in the lookup field which makes it easier to find a special record.
https://docs.microsoft.com/en-us/dynamics365/sales-professional/use-lookup-fields-forms
Hope it helps.
Best Regards,
Leo