Revenue has pressed ahead with the appointment of extra staff in preparation for a no-deal Brexit.
Over 500 appointments have been made since January.
In September last year, the Government granted approval for the phased recruitment of an additional 600 Revenue staff to meet the challenges posed in the case of a no deal.
Budget 2019 provided Revenue with the funding needed for 270 of the additional 600 staff, to manage an orderly UK withdrawal.
In March, prior to the agreed Brexit extention, Minister for Finance Paschal Donohoe said Revenue was on track to appoint 400 additional staff in customs and related roles by the end of March.
Since then the Brexit deadline has been extended to 31 October, but Revenue has continued to appoint staff from open recruitment and interdepartmental competitions,
450 additional staff have been assigned Customs related roles, the majority of whom completed initial training in April 2019.
They are deployed across a range of functions according to Revenue, with the majority assigned to import and export trade facilitation activities and policy and operational roles.
New staff are being "mentored" by experienced Customs staff to "enhance" their customs competency and are also receiving additional training on "Revenue enforcement procedures and Revenue systems".
Revenue said resources will be deployed based on the evolving business needs and to tackle any risks as they emerge.
It said it intends to continue to adjust its recruitment and training plans in response to business needs, including Brexit-related developments.
"The impact of the decision to extend the deadline on Brexit to 31 October 2019 is being assessed by Revenue having regard to resources, infrastructure and trader engagement".
It said that this will include broadening the scope of training for new staff, to include customs and other compliance functions as appropriate, based on business need.
It is also continuing to work with businesses on the steps they should be taking to prepare for Brexit.