To put things clear, you have more than 1 answer for this question
1) Feasibility - YES
2) Practicality - MAY BE
3) Worthiness - NO
Any base model can be converted to Top variant with all features. All that you need is more Vitamin-M. If safety feature is standards across variants and the difference is only the comfort features list, this task will be easy (comparatively) and will be cheaper than the OE Top end variant compromising / risking the Warranty. If the case is like upgrading the safety features as well, again it can be done, but sometimes you need to stripe down the car to skeleton to get it done, which will end up at a cost higher than OE Top spec. Adding ABS / Airbag to a base model is not something impossible, it's possible but not VFM / Worthy. All necessary parts along with ECUs (and sometimes additional body structures also) are required along with a skilled mechanic. In simple, it won't be just adding few parts, it will involve replacing most of the existing parts and hence time & money consuming.