controller.cls

	public String etFirstWarning {
    get { return [SELECT DeveloperName, Subject, Body FROM EmailTemplate WHERE DeveloperName = 'invoiceFirstWarning' LIMIT 1].Body;}
		set { etFirstWarning = value;}
	}
  
	public String etSecondWarning {
		get{
			return [SELECT DeveloperName, Subject, Body FROM EmailTemplate WHERE DeveloperName = 'invoiceSecondWarning' LIMIT 1].Body;
		}
		set{ etSecondWarning = value; }
	}

public void saveEmailSettings(){
		String s1 = etFirstWarning;
		String s2 = etSecondWarning;
		accounting_Controller.updateEmailTemplates(new List<String>{s1, s2});

		if (emailService.Boolean_Value__c != emailServiceCurrentSetting){
			if (emailService.Boolean_Value__c == false){
				String jobId = Setting__c.getInstance('Email Service').Text_Value__c;
				if (String.isNotBlank(jobId) ){
					System.abortJob(jobId);
				}
				System.debug('aborted job');
			} else {
				scheduleReminder sr = new scheduleReminder();
				String sch = '0 0 23 * * ? *';
				String jobId = System.schedule('Daily Email', sch, sr);
				emailService.Text_Value__c = jobId;
				System.debug('started job: ' + jobId);
			}
		}
    upsert emailService;
		if (invoiceMeta1.Text_Value__c.length() > 255 || invoiceMeta2.Text_Value__c.length() > 255){
			apexPages.addMessage( new apexPages.Message(apexPages.severity.info,'Length of invoice message must be 255 characters or fewer.'));
		} else {
			upsert invoiceMeta1;
			upsert invoiceMeta2;
		}
}
                                      
  @future
	public static void updateEmailTemplates(List<String> emailMessages){
		List<EmailTemplate> etList = [SELECT DeveloperName, Subject, Body FROM EmailTemplate WHERE DeveloperName = 'invoiceFirstWarning' OR DeveloperName = 'invoiceSecondWarning'];
		System.debug('these are the updated strings');
		System.debug(emailMessages);

		for (EmailTemplate et : etList){
			if (et.DeveloperName == 'invoiceFirstWarning') et.Body = emailMessages[0];
			else if (et.DeveloperName == 'invoiceSecondWarning') et.Body = emailMessages[1];
		}

		update etList;
	}