# Temporarily Changing the Value of a Tag in a UDT

**URL:** <https://forum.inductiveautomation.com/t/temporarily-changing-the-value-of-a-tag-in-a-udt/102329>\
**Category:** Ignition\
**Tags:** ignition81, perspective\
**Created:** [February 13, 2025, 6:05pm UTC](https://forum.inductiveautomation.com/t/temporarily-changing-the-value-of-a-tag-in-a-udt/102329 "2025-02-13T18:05:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![r123](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@r123](https://forum.inductiveautomation.com/u/r123)\
**Post date:** [February 13, 2025, 6:05pm UTC](https://forum.inductiveautomation.com/t/temporarily-changing-the-value-of-a-tag-in-a-udt/102329/1 "2025-02-13T18:05:53Z")

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I'm not thrilled with any approach so far, but I'm looking for the least painful solution.

I have a UDT containing several OPC tags, each with an associated expression tag that modifies its quality. The status and value of these expression tags are used in the application.

Now, I need to add a new tag pair to the UDT, but I want to force its value until real data is available from the field device.

My current idea is to initially set the new OPC or expression tag as a memory tag when updating the UDT, then switch it back once real data becomes available. Ideally, each instance would have a unique initial value.

Another option could be adding an `if` condition to the expression tag that checks a memory tag. If true, it would use a predefined value instead of live data.

KEPServerEX is the OPC server, and has a simulation driver that I'd have to path to or simulated mode for the device, but I only need to force a single tag, not the entire device.

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**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [February 13, 2025, 6:27pm UTC](https://forum.inductiveautomation.com/t/temporarily-changing-the-value-of-a-tag-in-a-udt/102329/2 "2025-02-13T18:27:44Z")

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Just make it a memory tag.

Later, change its "Value Source" to OPC and fill in the OPC properties.

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**Author:** ![r123](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@r123](https://forum.inductiveautomation.com/u/r123)\
**Post date:** [February 13, 2025, 9:33pm UTC](https://forum.inductiveautomation.com/t/temporarily-changing-the-value-of-a-tag-in-a-udt/102329/3 "2025-02-13T21:33:27Z")

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Now I just need a cool way to give each a unique default value. I'll probably just write a script to change them.